MFC r312118,r312121:

r312118:

Fix -Wformat issue with zero-length format string passed to err(3)

Tested with: clang, gcc 4.2.1, gcc 4.9

r312121:

Follow up to r312118

State that execve failed instead of just printing out the program name
and strerror(errno) via err(3).

MFC r282061:

Integrate tools/regression/execve into the FreeBSD test suite as
tests/sys/kern/execve

Integrate tools/regression/execve into the FreeBSD test suite as
tests/sys/kern/execve

MFC after: 1 week

Integrate tools/regression/execve into the FreeBSD test suite as tests/sys/kern/execve

Integrate more tests into the FreeBSD test suite from tools/regression, etc

o Add various regression tests for execve(2) syscall.

Obtained from: NetBSD