check-non-portable-shell.pl: `wc -l` may have leading WS

check-non-portable-shell.pl: `wc -l` may have leading WS

Test scripts count number of lines in an output and check it againt
its expectation.  fb3340a6 ("test-lib: introduce test_line_count to
measure files", 2010-10-31) introduced a helper to show a failure in
such a test in a more readable way than comparing `wc -l` output with
a number.

Besides, on some platforms, "$(wc -l <file)" is padded with leading
whitespace on the left, so

	test "$(wc -l <file)" = 4

would not work (most notably on macosX); the users of test_line_count
helper would not suffer from such a portability glitch.

Add a check in check-non-portable-shell.pl to find '"' between
`wc -l` and '=' and hint the user about test_line_count().

Signed-off-by: Torsten Bögershausen <tboegi@web.de>
Reviewed-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Helped-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>