Release Candidate of WebIssues Client 0.9.3

The release candidate for version 0.9.3 fixes a build error occurring on some platforms (thanks to hlamer for spotting and fixing it) and also some compilation warnings. In addition I made some code clean-ups and optimizations in a few places. No new functionality was added compared to the last beta version. The final version, which I expect to be released by the end of this month, will contain updated manual and translations; I'm also going to update the website a little bit and immediately start developing the next version of both client and server.