trace: cosmetic fixes for error messages

The error messages for the trace code are often multi-line;
the first line gets a nice "warning:", but the rest are
left-aligned. Let's give them an indentation to make sure
they stand out as a unit.

While we're here, let's also downcase the first letter of
each error (our usual style), and break up a long line of
advice (since we're already using multiple lines, one more
doesn't hurt).

We also replace "What does 'foo' for GIT_TRACE mean?". While
cute, it's probably a good idea to give more context, and
follow our usual styles. So it's now "unknown trace value
for 'GIT_TRACE': foo".

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

trace.c

@@ -61,8 +61,8 @@ static int get_trace_fd(struct trace_key *key)
 	else if (is_absolute_path(trace)) {
 		int fd = open(trace, O_WRONLY | O_APPEND | O_CREAT, 0666);
 		if (fd == -1) {
-			warning("Could not open '%s' for tracing: %s\n"
-				"Defaulting to tracing on stderr...",
+			warning("could not open '%s' for tracing: %s\n"
+				"         Defaulting to tracing on stderr...",
 				trace, strerror(errno));
 			key->fd = STDERR_FILENO;
 		} else {
@@ -70,11 +70,11 @@ static int get_trace_fd(struct trace_key *key)
 			key->need_close = 1;
 		}
 	} else {
-		warning("What does '%s' for %s mean?\n"
-			"If you want to trace into a file, then please set "
-			"%s to an absolute pathname (starting with /).\n"
-			"Defaulting to tracing on stderr...",
-			trace, key->key, key->key);
+		warning("unknown trace value for '%s': %s\n"
+			"         If you want to trace into a file, then please set %s\n"
+			"         to an absolute pathname (starting with /)\n"
+			"         Defaulting to tracing on stderr...",
+			key->key, trace, key->key);
 		key->fd = STDERR_FILENO;
 	}
 
@@ -93,7 +93,7 @@ void trace_disable(struct trace_key *key)
 	key->need_close = 0;
 }
 
-static const char err_msg[] = "Could not trace into fd given by "
+static const char err_msg[] = "could not trace into fd given by "
 	"GIT_TRACE environment variable";
 
 static int prepare_trace_line(const char *file, int line,