Remove mostly-unused (and unneeded) 'seq' member from 'sc' struct
Change 'keystr' member of 'sc' struct to be a std::string
Change which version of the onekey() function has the code and which delegates
Remove version of onekey() that accepted char*
Convert 'last_search' global from a char* to an std::string
Convert 'last_replace' global from a char* to an std::string
Remove empty search_init_globals() function
Use std::string for filenames in files.cpp
Convert locking_prefix and locking_suffix to std::string