test-lint: detect 'export FOO=bar'

Some shells do not understand the one-line construct, and instead need

  FOO=bar &&
  export FOO

Detect this in the test-lint target.

Signed-off-by: Thomas Rast <trast@inf.ethz.ch>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/check-non-portable-shell.pl

@@ -21,6 +21,7 @@ sub err {
 	/^\s*declare\s+/ and err 'arrays/declare not portable';
 	/^\s*[^#]\s*which\s/ and err 'which is not portable (please use type)';
 	/test\s+[^=]*==/ and err '"test a == b" is not portable (please use =)';
+	/^\s*export\s+[^=]*=/ and err '"export FOO=bar" is not portable (please use FOO=bar && export FOO)';
 	# this resets our $. for each file
 	close ARGV if eof;
 }