Update gnulib
m4/.gitignore: update from gnulib
astr.c: add missing call to GC_init
Fix FIXME: make estr opaque

A few other minor clarifications
Update and compress copyright ranges.
Rename castr to const_astr for clarity
region.c: fix incorrect attribute
configure.ac: remove test for -fmudflap, removed in GCC 4.9
Fix all but one remaining warnings, and some bugs

Most of the warnings and all of the bugs are to do with printf formats.
Hooray for GCC's attributes that allow user functions' formats to be
checked!
Add a const_estr type, analogous to const_astr

There's no function that creates them, but it makes it possible to
annotate functions that don't modify estr arguments.
Fix some warnings when building the astr test program
Remove references to freeing memory
Use bool everywhere a boolean is meant, not int
NEWS: add more for 2.4.10
Fix FIXME: make all struct types opaque pointer types
variables.c: fix a wrong-size allocation
Use enums more intelligently
Simplify to a single caller of undo_start_sequence and undo_end_sequence
funcs.c: make width condition for calling fill_break_line always the same

There was a +1 in this case.
funcs.c: give more accurate feedback when fill-column is set

If its previous value was not a number, it will now be shown correctly.