adblock slow on .*.*.*. rule

[Andrey Zholos]

Since updating to Midori 0.5.8, the browser hangs for several seconds when
opening any page.

I noticed this warning (it doesn't always appear):
WARNING **: subscriptions.vala:388: Adblock match error: Error while matching regular expression ..*..*..*.info/: backtracking limit reached

And found the corresponding rule in the filter list:
https://ruadlist.googlecode.com/hg/advblock.txt
.*.*.*.info/$popup

I think those dots should be escaped when building the regular expression.

This change to fixup_regex fixed the problem for me:

--- extensions/adblock/extension.vala
+++ extensions/adblock/extension.vala
@@ -464,6 +464,7 @@
                 case '?':
                 case '[':
                 case ']':
+ case '.':
                     fixed.append_printf ("\\%c", c); break;
                 default:
                     fixed.append_c (c); break;

This problem didn't seem to occur in previous versions of Midori, even though
the C version of fixup_regex also didn't escape dots. I'm not sure why that is.