Comment 4 for bug 834427

I'm pretty sure this is a case of backtracking run amok. An upstream
bug has already been filed: https://bitbucket.org/birkenfeld/pygments-main/issue/697/bad-regexp-in-perllexer

There is already a maximum file size the code will highlight, but
setting it even lower won't help; even very small files can cause this
problem (see the bug report for an example).