AST_EXT_LIB_CHECK has several optional parameters. When an optional parameter
is left empty, [] is used to indicate this. However, this is done in the script
./configure only then, when a further parameter is not empty. For example, when
no extra libraries are needed to test the checked library, parameter 5 is not
mentioned. Except parameter 6 and higher are used, then parameter 5 must be
empty.

However, this general rule was broken
* four times for parameter 5 (extra libs) and
* three times for parameter 4 (header)
as found via the Regular Expression \[\]\). In case of parameter 5, all cases
were changed, because that happened for no reason. In case of parameter 4, an
[] improves readability actually. Therefore for parameter 4, the only case which
did not do it was changed. All this aims to create more consistency: Only do
something different if there is a reason to do so.

Change-Id: I037ef170cf1ad94497151a9ea5071a31c656cafe

Remove symbols that are depreacated and replaced:
* ast_channel_datastore_alloc
* ast_channel_datastore_free
* ast_channel_cmpwhentohangup
* ast_channel_setwhentohangup
* config_text_file_save
* devstate2str
* ast_device_state_changed
* ast_device_state_changed_literal
* ast_verbose_get_by_module

Remove unused symbols:
* channelreloadreason2txt (last used in Asterisk 12).

Remove unused ast_options flags:
* AST_OPT_FLAG_END_CDR_BEFORE_H_EXTEN / ast_opt_end_cdr_before_h_exten
* AST_OPT_FLAG_VERBOSE_MODULE / ast_opt_verb_module
* AST_OPT_FLAG_INITIATED_SECONDS

Change-Id: I841255995d195f8efc1ed47af9c7a2f131c08645

* dahdi_chan_name
* dahdi_chan_name_len
* dahdi_chan_mode
* __manager_event
* dialed_interface_info

Added comment about __progname and environ being needed for FreeBSD to
prevent accidental removal in the future.

Change-Id: I3ae026bc541cd9cb572be2ffa95fc359547642b5

Change-Id: I317a82de976bbdbfe4352c243e32a7bb8f66c377

Change-Id: I140e1137906bbfcdb61c0c6304159be459ad873e

If the two formats on a channel are equal, we don't transcode and since
the generic plc needs slin to work, it doesn't get invoked.

* A new configuration option "genericplc_on_equal_codecs" was added
  to the "plc" section of codecs.conf to allow generic packet loss
  concealment even if no transcoding was originally needed.
  Transcoding via SLIN is forced in this case.

ASTERISK-27743

Change-Id: I0577026a179dea34232e63123254b4e0508378f4

Change-Id: I658141c6ec490a3e866b02d2afea757928ceaabf

Change-Id: I5133ff2ba4e030f9733fb3d050c863d72a22ae6b

Change-Id: I3775a696d6a57139fdf09651ecb786bcf1774509

* Define CHAR_T_LIBEDIT and CHAR_TO_LIBEDIT based on
  HAVE_LIBEDIT_IS_UNICODE.  This avoids needing to repeatedly use
  conditional blocks, eliminates having multiple function prototypes.
* Remove parenthesis from return values.
* Add missing code block brackets {}.
* Reduce use of 'else' conditional statements where possible.

Change-Id: I4315328ebea2f62641faf6881de2ac20a9f9d08e

Asterisk uses various symbols of the shared library libogg within the module
format_ogg_vorbis. However, the source code of that module did not include the
header file of libogg explicitly but implicitly. Because that header was not
included before Asterisk 14, the script ./configure was told not to check for
it.

Anyway, even Asterisk 13 LTS uses symbols of libogg. Therefore, that header
should be included explicitly. Therefore, ./configure should check for that
header.

Change-Id: I98c50d56311b68880d1084fcc62c35ab2f8692db

./configure --with-pjproject-bundled
did not display an explanation, when no download utility like wget, curl, or
fetch was installed beforehand, although an explanation existed in code. This
happened because the code expected the variable DOWNLOAD_TO_STDOUT to be empty.
However, the script ./configure set that variable always.

Change-Id: I64c99b76a03525c69471e5055bf124b36a51bbd4

Asterisk does not need the development package of libltdl, because it does not
use any symbol of -lltdl directly. Instead, it uses the runtime package via the
shared library -lodbc. On the supported platforms, that shared library declares
its dependency on -lltdl correctly, otherwise AST_EXT_LIB_CHECK would have
failed.

ASTERISK-27745

Change-Id: Icd315809b8e7978203431f3afb66240dd3a040ba

Change-Id: I0e2402660e54d91f74ab0804c62a5b1925577413