Fix formatting for couple of docs in the compiler

Source code on scaladoc for the virtual pattern matcher was not being
correctly identified as such. Also, I had to use an html code tag instead
of backticks when referring to the __match identifier, otherwise the
double underscore would be treated as start-of-underline wiki markup.
Merge pull request #2526 from dcsobral/doc/patMat

Fix formatting for couple of scaladocs in the compiler