Require automake 1.14 and autoconf 2.65

Require automake 1.14 and autoconf 2.65

This allows to fix distclean properly, since we know that
subdir-objects is used. When it is the case, it is not a good idea for
a Makefile to use a source file which is under the control of another
one. This could not be made to work work with old automake versions
(<1.14).

Therefore we refer directly to object files in Makefile.am instead of
source files. The actually leads to less compilation in tex2lyx.

Update the code here and there to remove compatibility hacks. Update
documentation.

Re-enable the layout test and fix the Length test, which was ovewriting
memory in test_inPixels() because lyxrc did not had a correct layout.