configure.ac: Require core CVS. This is implicit in the -base CVS requirement alread...

configure.ac: Require core CVS.  This is implicit in the -base CVS requirement already, so we might just well spell i...

Original commit message from CVS:
* configure.ac:
Require core CVS.  This is implicit in the -base CVS
requirement already, so we might just well spell it
out.  Also, we do need at least 0.10.14 for
gst_element_class_set_details_simple().  Make check
for gmyth a bit more restrictive so things don't break
if the next version changes API.
* ext/alsaspdif/alsaspdifsink.c:
Work around alsa alloca macros triggering 'always evaluates to
true' warnings with gcc-4.2 and fix compilation with gcc-4.2.
Also don't leak the device string.
* ext/mpeg2enc/gstmpeg2enc.cc:
* ext/soundtouch/gstpitch.cc:
* gst/modplug/gstmodplug.cc:
Fix compilation with g++4.2 and -Wall -Werror (also needs plugin
define fix from core CVS). Fixes #462737.