to the current Python interpreter (ie. the one used for
building/installation), even (especially!) if "/usr/bin/env" appears in
the #! line.
Rationale: installing scripts with "#!/usr/bin/env python" is asking for
trouble, because
1) it might pick the wrong interpreter (not the one used to
build/install the script)
2) it doesn't work on all platforms (try it on IRIX 5, or on Linux
with command-line options for python)
3) "env" might not be in /usr/bin
* 'first_line_re' loosened up
* command description improved
* replaced '_copy_files()' and '_adjust_files()' with one method
that does everything, 'copy_scripts()' -- this should be more
efficient than Bastian's version, should behave better in
dry-run mode, and does timestamp dependency-checking