execve.2, pipe.2, tee.2, fmemopen.3, mq_notify.3, qsort.3: Replace use of assert...

execve.2, pipe.2, tee.2, fmemopen.3, mq_notify.3, qsort.3: Replace use of assert() by code that checks argc

See http://bugzilla.kernel.org/show_bug.cgi?id=13569

As noted by Andrey:
The purpose of the assert macro, defined in <assert.h>,
is to provide a tool to check for programming mistakes
or program logic errors. However, the assert macro must
never be used to perform checks for run time errors,
since, with the NDEBUG macro defined, expressions within
the assert macro invocations are not evaluated/checked
for, resulting in behavior that was not originally intended.
...
The pages affected in the core package are

execve(2)
pipe(2)
tee(2)
fmemopen(3)
mq_notify(3)
qsort(3)

Reported-by: Andrey Vihrov <vihrov@gmail.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>