Check for sinh(), cosh() and asinh() and define our own implementations if they're not available. Fixes bug #520880.

Original commit message from CVS:
* configure.ac:
* gst/audiofx/Makefile.am:
* gst/audiofx/audiochebband.c:
* gst/audiofx/audiocheblimit.c:
* gst/audiofx/math_compat.h:
Check for sinh(), cosh() and asinh() and define our own
implementations if they're not available. Fixes bug #520880.