Programs that want to background themselves now need
to define threadmaybackground returning 1.
This avoids a confusing (to people and debuggers)
extra parent process for all the threaded programs
that will never want to background themselves.

Remote whitespace at the ends of lines.
Remove blank lines from the ends of files.
Change modes on source files so that they
are not executable.

Signed-off-by: Dan Cross <cross@gajendra.net>

When fetching, messages are sent to plumber as soon as the ENVELOPE part is read.
    The date field of the message is sent when the INTERNALDATE part is read and
    there is no guarantee that this will be read before the ENVELOPE.
    This bug can be observed when using faces(1) which will retrieve messages with
    a null date and then always display a 'Jan 1' date instead of the correct one.
    The fix is to simply send the message to plumber after having read all parts,
    thus ensuring the message is complete.

Both `upas/nfs` and `upas/smtp` call the currently broken `tlsClient()`
from libsec. This commit copies a fix from upas/nfs into upas/smtp.

In `imapdial()`, upas/nfs replaces a process call for tlsClient with
`stunnel3` when not on Plan 9. upas/smtp calls tlsClient directly
as a function, so imapdial was copied into mxdial.c as `smtpdial()`,
and tlsClient+dial replaced with a call to smtpdial.

According to RFC 3501 the arguments to the LOGIN command should be
quoted strings (or length prefixed string literals). Without quoting,
authentication to some IMAP servers (e.g. Dovecot) will fail.

decode.c:146:8: warning: variable ‘argv’ set but not used
fs.c:953:47: warning: variable ‘reset’ set but not used
imap.c:348:6: warning: variable ‘prefix’ set but not used

Updates #114.

Do not hardcode stunnel directory path, just make sure that is installed
in user '$PATH'. it is required for 'mailfs -t' TLS support, so printout
an error string if it was not found.

Tested with latest stunnel version 5.17 on OpenBSD and macosx.

% mailfs -t imap.gmail.com ; echo $?
0

Change-Id: Icbd507c7efa81ef2aa7aed37bec5f639b37526cb
Reviewed-on: https://plan9port-review.googlesource.com/1280
Reviewed-by: Russ Cox <rsc@swtch.com>

R=rsc
https://codereview.appspot.com/92650043

TBR=rsc
https://codereview.appspot.com/107760043