Support "// recheck" comments

[tebeka]

We currently check the regexp functions. However there are many other functions that get a string and compile it to a regular expression, notably routers such as gorilla/mux.

I suggest supporting a special comment that will tell us this function call is also using a regular expression.

• // recheck will check first argument
• // recheck 2` will check argument in offset 2 (third)

Maybe also a flag to tell if it's Go or POSIX format.