Add support for long options

Add support for long options

Recognize --help and --version options as aliases to -h and -V options,
respectively.

* strace.c: Include <getopt.h>.
(init): Move short options to optstring, add longopts array, use
getopt_long instead of getopt.
(usage): Document --help and --version options.
* strace.1.in: Likewise.
* tests/strace-V.test: Check that "strace --version" output is the same
as "strace -V" output.