Fix MSIE conditionals regex in minify output

Some MSIE conditional comments are mangled when minify_content is
enabled, which causes the entire document to be treated as if it is
commented.

Don't know how often pyro updates it's copy of codeigniter, but I have
also submitted this change to EllisLab/CodeIgniter#2120
Merge pull request #2199 from mikezilla/2.2/feature/MSIE-conditionals

Fix MSIE conditionals regex in minify output