Changed autogen.sh to bail out if necessary tools can't be found

Changed autogen.sh to bail out if necessary tools can't be found
instead of proceeding to the version checks.

Document use of autogen.sh in README.

Generate check.spec from check.spec.in to it automatically gets the
correct version number.

Generate check.h from chech.h.in and include Check version information.

Compile Check version number into the library to allow for runtime
version checks.

Added the m4 script check.m4 that allows to easily integrate Check
into projects using autoconf/automake. It does version checking and
also assures that header and library versions match.

Document the use of check.m4 and the AM_PATH_CHECK() macro in the
tutorial. Adapted example Makefile.am and configure.in and added a
missing .cvsignore file.

git-svn-id: svn+ssh://svn.code.sf.net/p/check/code/trunk@124 64e312b2-a51f-0410-8e61-82d0ca0eb02a