Use extglob rather than regex match operator.

[jfgoog]

Not all shells support =~. Android, for example, uses mksh, which does
not.

Change is from suggestion at http://www.mirbsd.org/mksh-faq.htm#regex-comparison

[landley]

They're not the same thing, would break sh.test "sh functions need block" test for example (looking for [Ss]yntax).

I replaced it with a call to grep -q in commit 1c74121

Hello github, I pushed the commit and edited to resave the message, please turn commit 1c74121 into a link.