use regex_compiler::operator[] to register named regexes, so a dynamic regex can invoke a static one

[SVN r37174]

libs/xpressive

@@ -1 +1 @@
-Subproject commit 0d18ca25c43506d0aa31235c5993836c5df97efd
+Subproject commit 53c5882fbea7eeb08223f8f162a34d9a5a14ff40