configure.ac: Bump requirement to core and -base >= 0.10.12 .

configure.ac: Bump requirement to core and -base >= 0.10.12 .

Original commit message from CVS:
* configure.ac:
Bump requirement to core and -base >= 0.10.12 .
* gst/Makefile.am:
* gst/gstversion.override.in:
* gst/gst-0.10.10.ignore:
* gst/gst-0.10.11.ignore:
* gst/gst-0.10.12.ignore:
* gst/gst-0.10.3.ignore:
* gst/gst-0.10.4.ignore:
* gst/gst-0.10.5.ignore:
* gst/gst-0.10.6.ignore:
* gst/gst-0.10.7.ignore:
* gst/gst-pb-0.10.11.ignore:
Remove no-longer needed files.