MFC r353325, r353875

r353325:
Update tcsh to 6.21.00.

This is a bugfix release with no new features. A number of these fixes
were previously merged into our tree.

Sponsored by: DARPA, AFRL

r353875:
Update tcsh to git revision 83c5be0 bringing in a number of bug fixes.

Reported by: sobomax
Sponsored by: DARPA, AFRL
Differential Revision: https://reviews.freebsd.org/D22099

Record prior MFC of r315948, r315952

MFC r315948:

Update tcsh to 6.20.00

MFC r315952:

Update tcsh to vendor git b605cb561d

Vendor changes:

1. PR/471: Daiki Ueno: Delay interpreting arginp until we've processed
our startup files (which can change the NLS environment).

2. Fix type of read in prompt confirmation (eg. rmstar) (David Kaspar).

3. Fix out of bounds read (Brooks Davis)
(reproduce by starting tcsh and hitting tab at the prompt).

4. Don't play pointer tricks that are undefined in modern c
(Brooks Davis).

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Update to tcsh 6.18.01.

Fix tcsh losing history when tcsh terminates because the pty beneath it
is closed.

Diagnosed by Ted Anderson:

New signal queuing logic was introduced in 6.15 and allows the signal handlers
to be run explicitly by calling handle_pending_signals, instead of
immediately when the signal is delivered. This function is called at
various places, typically when receiving a EINTR from a slow system call
such as read or write. In the pty exit case, it was called from xwrite,
called from flush, while printing the "exit" message after receiving EOF
when reading from the pty (note that the read did not return EINTR but
zero bytes, indicating EOF). The SIGHUP handler, phup(), called
rechist, which opened the history file and began writing the merged
history to it. This process invoked flush recursively to actually write
the data. In this case, however, the flush noticed it was being called
recursively and decided fail by calling stderror.

My conclusion was that the signal was being handled at a bad time. But
whether to fix flush not to care about the recursive call, or to handle
the signal some other time and when to handle it, was unclear to me.
However, by adding an extra call to handle_pending_signals, just after
process() returns to main(), I was able to avoid the truncated history
after network outages and similar failures. I verified this fix in
version 6.17.

Approved by: ed (mentor)
MFC after: 1 week

Update to tcsh 6.17.00.

Approved by: re (kensmith)

Actually fix pty detection for autologout setting.
(The fix has been submitted upstream.)

This commit was generated by cvs2svn to compensate for changes in r172665,
which included commits to RCS files with non-trunk default branches.

Import two vendor fixes from tcsh-6.15.01 for MFC to 7.0. The fixes are:
- Fix pty detection for autologout setting
- kill `foo` got stuck because sigchld was disabled too soon

Requested by: re

Import of tcsh-6.15.00

Import of tcsh-6.14.00

Import of tcsh-6.13.00

Import of tcsh-6.12.00

Import tcsh-6.11

Import vendor fix for buffer overflow in HOME environment variable

Initial import of slightly trimmed tcsh 6.10

6.09.01 vendor update.

Import the latest version of the 44BSD C-shell -- tcsh-6.09.