Misleading indentation warnings are actually useful, as they
will occasionally reveal actual bugs (cf the apple `goto fail`
security bug from a few years ago).  Newer versions of clang
(at least) are more aggressive about warnings in this regard,
which has exposed a few warnings that are annoying.  However,
they are easy to address.

commit 385a6d5877258cee0cac6151e6359c9206006b01 removed src/lib9p/_post.c
from the code base, but overlooked removing a reference to the
_post.o object file from the src/lib9p/mkfile.

This results in lib9p failing to compile:

* Running on Darwin...
* Compiler version:
	Apple clang version 12.0.5 (clang-1205.0.22.11)
* Building mk...
* Building everything (be patient)...
>>> mk: don't know how to make '/Users/sasha/plan9port_fork/lib/lib9p.a(_post.o)' in /Users/sasha/plan9port_fork/src/lib9p
mk: for i in ...  : exit status=exit(1)

Remove _post.o from the list of dependent object files from
src/lib9p/mkfile to have lib9p compile.

Fixes: 385a6d587725 ("lib9p: Remove postmountsrv (#505)")

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>

R=rsc
http://codereview.appspot.com/6744054

thanks to Erik Quanstrom

R=rsc
http://codereview.appspot.com/3469042