Fix some localtime.c problems noted by Christos Zoulas

in: http://mm.icann.org/pipermail/tz/2014-October/021684.html
* localtime.c (tzload): Use ssize_t, not int.  Redo comparison to
avoid the need for an ssize_t value less than -1, which POSIX does
not guarantee.  Use memmove so that we needn't worry about an
ssize_t index.
(tzparse): Remove static always-zero var.  Initialized fields
to zero by hand instead.
(zoneinit): Initialized more fields, to avoid undefined behavior
in tzalloc.
(leapcorr): Fix bug, a stray initialization of a local variable.
* Makefile: Add comment about ssize_t.
* NEWS: Document the above.