Statistics for the gtk3-demo listbox example show that the
vast majority of calls to _gtk_allocated_bitmask_resize go
from a size of 2 to 2. Don't needlessly call realloc() in
this case.
The speed-up in 7da1f8a1ce was wrong in
certain conditions, even though it didn't trigger the existing
testsuite.
New testcase /bitmask/invert_range_hardcoded included.
This does nothing but turn all GtkBitmask functions into static inline
functions that call the gtk_allocated_bitmask_*() equivalent.
The implementation of the static functions has also been put into a
private header, to not scare people who want to see how things are
implemented.
