Use a POSIX sh on Solaris

As described elsewhere[1], Solaris' `/bin/sh` is not POSIX, but `/usr/xpg4/bin/sh` is. Change the shebang line in all scripts to use that.

There must be a way to make autotools handle this for us.

[1]: http://books.google.se/books?id=Df7P1WyG87sC&pg=PA4&lpg=PA4&dq=solaris+sh+backticks&source=bl&ots=dvSrtqCIEH&sig=srAdFmHcadAjq1HioAIoIa1urUc&hl=en&sa=X&ei=h2YQU97dF6Kj4gS--YHYBA&redir_esc=y#v=onepage&q=solaris%20sh%20backticks&f=false