regexp funcs versus '\0'

[Kevin Ryde]

When calling a C function that expects a '\0' terminated string, I
wonder if the guile string should be checked and an error thrown if
there's a \0 (apart from the terminator).  That'd ensure the input
doesn't get silently "truncated".

I noticed this in the regexp matching functions, where I was trying
each possible character as a test, and #\nul didn't work.