Compat fix for building against 4.9

c_sizeof_or_alignof_type changed signature in 4.9; update
accordingly.
Testsuite fixes for building against 4.9
Prepare for 0.13 release
lxml is a dependency
python 3 fixes
Add plugin python directory to python modules search path to fix 'gccutils not found' error
Fix crashing on expr 'var = {CLOBBER};', because location of such expression has NULL filename
Fix exception in case of unrecognized source file encoding