Installed devinclude headers have conditional code depending on options
detected at configure time. This header is needed in the prefix to match
those ones to the installed libraries.

Fixed various problems in *.m4 files.
Organized a bit further configure.ac file.
Added common.in to .gitignore and deleted an unexistent file entry.

Fix CRegions size calculation

This reverts commit 072ac697, reversing
changes made to 9a87a06f.

* Added .gitignore