chainlint.sed: stop splitting "(..." into separate lines "(" and "..."

Because `sed` is line-oriented, for ease of implementation, when chainlint.sed encounters an opening subshell in which the first command is cuddled with the "(", it splits the line into two lines: one containing only "(", and the other containing whatever follows "(". This allows chainlint.sed to get by with a single set of regular expressions for matching shell statements rather than having to duplicate each expression (one set for matching non-cuddled statements, and one set for matching cuddled statements). However, although syntactically and semantically immaterial, this transformation has no value to test authors and might even confuse them into thinking that the linter is misbehaving by inserting (whitespace) line-noise into the shell code it is validating. Moreover, it also allows an implementation detail of chainlint.sed to seep into the chainlint self-test "expect" files, which potentially makes it difficult to reuse the self-tests should a more capable chainlint ever be developed. To address these concerns, stop splitting cuddled "(..." into two lines. Note that, as an implementation artifact, due to sed's line-oriented nature, this change inserts a blank line at output time just before the "(..." line is emitted. It would be possible to suppress this blank line but doing so would add a fair bit of complexity to chainlint.sed. Therefore, rather than suppressing the extra blank line, the Makefile's `check-chainlint` target which runs the chainlint self-tests is instead modified to ignore blank lines when comparing chainlint output against the self-test "expect" output. This is a reasonable compromise for two reasons. First, the purpose of the chainlint self-tests is to verify that the ?!AMP?! annotations are being correctly added; precise whitespace is immaterial. Second, by necessity, chainlint.sed itself already throws away all blank lines within subshells since, when checking for a broken &&-chain, it needs to check the final _statement_ in a subshell, not the final _line_ (which might be blank), thus it has never made any attempt to precisely reproduce blank lines in its output. Signed-off-by: Eric Sunshine <sunshine@sunshineco.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>