patch: if reading fails, do not go into infinite loop asking for a filename.

This can happen if no tty is available.

Obtained from:	OpenBSD (CVS rev 1.54)

patch(1): make some macros look boolean.

Minor cleanup inspired by a new patch(1) variant in schily tools.

For reference:
https://sourceforge.net/p/schillix-on/

patch(1): avoid signed integer overflow when debugging.

Integer i is used to index p_end of type LINENUM (actually long).
Match the types.

  Fix a ton of speelling errors

patch(1): small include changes.

Mostly to match OpenBSD, no functional change.

MFC r286601 + 286617:

use posix_spawn(3) instead of fork() and exec() manually as suggested
by jmg@.

Fix routed remote denial of service vulnerability. [SA-15:19]

Fix resource exhaustion in TCP reassembly. [SA-15:15]

Fix OpenSSH multiple vulnerabilities. [SA-15:16]

patch: Bring in xstrdup and use it when appropriate.

The function savestr allows NULL return values during Plan A patching so in
case of out of memory conditions, Plan B can step in.  In many cases, NULL
value is not properly handled, so use xstrdup here (it's outside Plan A/B
patching, which means that even Plan B relies on successful operations).

Clean up some whitespaces while here

Obtained from:	OpenBSD

Minor fixes to exit status.

Exit with EXIT_FAILURE for invalid arguments.
Fixes NetBSD-PR 43517.

Print version string to stdout instead of stderr;
it is user-requested and not an error.

Obtained from:	NetBSD

patch(1): Bring fixes from OpenBSD

Check fstat return value.  Use off_t for file size and offsets.
Avoid iterating over end of string.

Introduce strtolinenum to properly check line numbers while parsing:
no signs, no spaces, just digits, 0 <= x <= LONG_MAX

Properly validate line ranges supplied in diff file to prevent overflows.
Also fixes an out of boundary memory access because the resulting values
are used as array indices.

PR:		195436
Obtained from:	OpenBSD