Caching

I’ve been fiddeling around with Courier over the last couple of days. One of the planned improvements is caching of pages in the history and it seems to work reasonably well now. One problem however resurfaced: The protoTXView can use a VBO to store large text files, but it seems to be somewhat unstable. Sometimes, the stored data gets corrupted, resulting in -10600 and -10061 errors. The workaround for now is to have either history caching or VBO usage.