REGEX Dialect

[mzuenni]

It is currently not specified what regular expression dialct is used, and this has already been changed in the past: fc72292

Note that this has many implications:

• \d vs [:digit:]
• longest vs first matching: REGEX("p|ps") RGEX("s") EOF will either accept ps or not
• a lot of common features are not present in ERE

What was the reason to switch from ECMAScript to ERE here? (ECMAScript would be the more natural choice IMO)