clang compiler warnings: Fix -Wabsolute-value warnings

This patch fixes several warnings caught by clang - in this case, usage of the
abs function on non-integer values. This patch uses labs and fabs, as
appropriate, in the various affected files.

Review: https://reviewboard.asterisk.org/r/4525

ASTERISK-24917
Reported by: dkdegroot
patches:
  rb4525.patch submitted by dkdegroot (License 6600)
........

Merged revisions 433749 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/13@433750 65c4cc65-6c06-0410-ace0-fbb531ad65f3