index: Don't bother indexing quoted portions of messages (and signatures).

Our old notmuch-index-message.cc code had this, but I originally
left it out when adding indexing back in. I was concerned primarily
with mistakenly detecting signature markers and omitting important
text, (for example, I often do long lines of "----" as section
separators).

But now I  see that there's a performance benefit to skippint the
quotations, (about 120 files/sec. instead of 95 files/sec.). I mitigated
the bogus signature checking by recognizing nothing other than the
all-time classic "-- ".

index.cc

@@ -135,6 +135,60 @@ skip_re_in_subject (const char *subject)
     return s;
 }
 
+/* Given a string representing the body of a message, generate terms
+ * for it, (skipping quoted portions and signatures).
+ *
+ * This function is evil in that it modifies the string passed to it,
+ * (changing some newlines into '\0').
+ */
+static void
+_index_body_text (notmuch_message_t *message, char *body)
+{
+    char *line, *line_end, *next_line;
+
+    if (body == NULL)
+	return;
+
+    next_line = body;
+
+    while (1) {
+	line = next_line;
+	if (*line == '\0')
+	    break;
+
+	next_line = strchr (line, '\n');
+	if (next_line == NULL) {
+	    next_line = line + strlen (line);
+	}
+	line_end = next_line - 1;
+
+	/* Get to the next non-blank line. */
+	while (*next_line == '\n')
+	    next_line++;
+
+	/* Skip blank lines. */
+	if (line_end < line)
+	    continue;
+
+	/* Skip lines that are quotes. */
+	if (*line == '>')
+	    continue;
+
+	/* Also skip lines introducing a quote on the next line. */
+	if (*line_end == ':' && *next_line == '>')
+	    continue;
+
+	/* Finally, bail as soon as we see a signature. */
+	/* XXX: Should only do this if "near" the end of the message. */
+	if (strncmp (line, "-- ", 3) == 0)
+	    break;
+
+	*(line_end + 1) = '\0';
+
+	_notmuch_message_gen_terms (message, NULL, line);
+    }
+}
+
 /* Callback to generate terms for each mime part of a message. */
 static void
 _index_mime_part (notmuch_message_t *message,
@@ -207,7 +261,7 @@ _index_mime_part (notmuch_message_t *message,
     g_byte_array_append (byte_array, (guint8 *) "\0", 1);
     body = (char *) g_byte_array_free (byte_array, FALSE);
 
-    _notmuch_message_gen_terms (message, NULL, body);
+    _index_body_text (message, body);
 
     free (body);
 }