This is just a straight refactoring. Various ad hoc string_*
functions that appeared in Common_utils have been renamed and placed
in the String.* namespace. The old vs "new" functions are:
string_prefix -> String.is_prefix
string_suffix -> String.is_suffix
string_find -> String.find
replace_str -> String.replace
string_nsplit -> String.nsplit
string_split -> String.split
string_lines_split -> String.lines_split
string_random8 -> String.random8
0944acf90c