The internal diff and merge machinery has been updated to use
standard size_t types rather than signed longs for buffer
allocations and offsets, preventing subtle overflow issues on LLP64
architectures, and plugging uninitialized memory leaks along error
paths.
* jk/xdiff-size_t:
merge-ll: report an error when reading external merge results fails
merge-ll: handle external driver status before reading result
merge-ll: use read_mmfile() to read external merge results
xdiff: NUL-terminate buffers read by read_mmfile()
xdiff: use size_t for buffer sizes
xdiff: replace mmbuffer_t with mmfile_t
xdiff: clean up read_mmfile() allocations on error
dfa7f97344