Port recent XCB changes to 64-bit ‘long int’

Port recent XCB changes to 64-bit ‘long int’

For historical reasons, libX11 represents 32-bit values like Atoms as
‘long int’ even on platforms where ‘long int’ is 64 bits.  XCB doesn’t
do that, so adapt the recent XCB code to behave properly on 64-bit
platforms.  Also, fix what appears to be a bug in the interpretation
of xcb_get_property_value_length, at least on my Fedora platform
which is running libxcb-1.11-5.fc21.
* src/xfns.c (x_real_pos_and_offsets):
* src/xterm.c (get_current_wm_state):
xcb_get_property_value_length returns a byte count, not a word count.
For 32-bit quantities, xcb_get_property_value returns a vector
of 32-bit words, not of (possibly 64-bit) long int.

Backport.