[perl #100232] Implementation details leak through in variable interpolation into regexes

[Larry Wall via RT]

A new restricted dialect of regex is implemented in 
28ab83f947b4899a4f8698eee5bc056742f356f1 and 
19d84be0066978f616ace6fa9f506e742161a378

Tests in 1becd7c9b456b707a14bfba40d672ec28945f199