Perform an operation on each config variable in given config backend matching a regular expression.
This behaviors like git_config_foreach_match
except instead of all config
entries it just enumerates through the given backend entry.
The regular expression is applied case-sensitively on the normalized form of the variable name: the section and variable parts are lower-cased. The subsection is left unchanged.
regular expression to match against config names (can be NULL)
the data to pass to the callback