#431 treat .make.log files right

[Lee Worden]

This should be a pretty small one. *.make.log files are treated like any other project file except that they're produced as side effects of PE make jobs, there are special links to them, and you don't make them directly. We suppress the "make" buttons on the directory listing for .make.log files. We should make sure that they don't go to make when used in project-file tags, retrieved by GetProjectFile, or any other time. Also make sure they don't get background make buttons.

In general, make sure people don't have to worry about weirdness when they use one.