Allow setting MaxFileUploads from .hdf

Summary: There used to be no limit, now its 20, and we can't control
it via hdf.

Reviewed By: @JoelMarcey

Differential Revision: D1618200
Cache results of pcre_fullinfo

Summary: pcre_fullinfo can be precomputed for a given compiled regular expression.

Reviewed By: @oyamauchi

Differential Revision: D1557859