Created attachment 344179 [details] [review]
Fix various potential compiler warnings

This is useful for a the next commit which switches away from
gnome-common and uses AX_COMPILER_FLAGS adding some new compiler
warning flags.

Created attachment 344180 [details] [review]
Port from gnome-common to autoconf-archive

See https://wiki.gnome.org/Projects/GnomeCommon/Migration

Visible changes:

* --enable-compile-warnings is now [no/auto/yes] instead of
  [no/minimum/yes/maximum/error]
* warnings are errors by default except for releases or if
  --disable-Werror is passed (which is the default in jhbuild)

AX_APPEND_COMPILE_FLAGS() gets used to disable some warnings enabled by
AX_COMPILER_FLAGS() because they trigger with pycairo/python headers.

Tested with gcc 6.3, clang 3.8.1

Created attachment 344181 [details] [review]
aclocal: make local file discover by reading AC_CONFIG_MACRO_DIR work

aclocal needs to know where the local macros are for including them and
for having a place to put the required system ones in.

Since 1.13 it can parse configure.ac and get the path from AC_CONFIG_MACRO_DIR.
This didn't work because for some reasons it complains if the local macros
start with "AM_" even if they are there (I guess it assumes they can't be local).
To work around that change the AM prefix to PYG.

To work around that, change the AM prefix to PYG, bump the automake version so
we can asume aclocal finds it and remove the hardcoded paths from both
autogen.sh and Makefile.am.