checkpatch: update signature "might be better as" warning

email header lines can look like signature tags.  It's valid to have
multiple email recipients on a single line but not valid to have multiple
signatures on a single line.

Validate signatures only when not in the email headers.

Clear the $in_commit_log flag when the patch filename appears.

Add '-' to the valid chars in a message header for headers
like "Message-Id:" and "In-Reply-To:".

Signed-off-by: Joe Perches <joe@perches.com>
Reported-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/checkpatch.pl

@@ -1504,9 +1504,11 @@ sub process {
 		if ($line =~ /^diff --git.*?(\S+)$/) {
 			$realfile = $1;
 			$realfile =~ s@^([^/]*)/@@;
+			$in_commit_log = 0;
 		} elsif ($line =~ /^\+\+\+\s+(\S+)/) {
 			$realfile = $1;
 			$realfile =~ s@^([^/]*)/@@;
+			$in_commit_log = 0;
 
 			$p1_prefix = $1;
 			if (!$file && $tree && $p1_prefix ne '' &&
@@ -1546,7 +1548,8 @@ sub process {
 		}
 
 # Check signature styles
-		if ($line =~ /^(\s*)($signature_tags)(\s*)(.*)/) {
+		if (!$in_header_lines &&
+		    $line =~ /^(\s*)($signature_tags)(\s*)(.*)/) {
 			my $space_before = $1;
 			my $sign_off = $2;
 			my $space_after = $3;
@@ -1623,7 +1626,7 @@ sub process {
 # Check if it's the start of a commit log
 # (not a header line and we haven't seen the patch filename)
 		if ($in_header_lines && $realfile =~ /^$/ &&
-		    $rawline !~ /^(commit\b|from\b|\w+:).+$/i) {
+		    $rawline !~ /^(commit\b|from\b|[\w-]+:).+$/i) {
 			$in_header_lines = 0;
 			$in_commit_log = 1;
 		}