add tcp_wrappers dependency to x11/gdm
Enabled gtk and urwid versions
Updated devel/bpython to 0.12nb1
Make xmlcatmgr and catalogs.mk cross-compilable.
Fix and tweak libX11 cross-build.

- Tool-depend on xproto for data for a tool that libX11 builds and
  runs.

- No need to pass CPPFLAGS_FOR_BUILD=-I${PREFIX}/include.

- Pass CC_FOR_BUILD=${NATIVE_CC:Q} in CONFIGURE_ENV, not MAKE_ENV.
Make libxcb and xcb-proto cross-compile.