Add --enable-dev-mode=strict to configure.

Passing -Wshadow to gcc enables shadow warnings.  From the gcc manual:

    Warn whenever a local variable or type declaration shadows another
    variable, parameter, type, or class member (in C++), or whenever a
    built-in function is shadowed.

Asterisk will not currently compile with this option set, but a number of bugs
have been discovered by enabling this flag on specific files.  The long-term
goal is to eliminate all of the suspect code that causes this warning to be
emitted.


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@358622 65c4cc65-6c06-0410-ace0-fbb531ad65f3