The switch is easier to understand than the side effects in the if
test. It also potentially allows us more flexibility in breaking up
this function into smaller pieces, since passing private_status around
is icky.
'database.cc' is becoming a monster, and it's hard to follow what the
various static functions are used for. It turns out that about 1/3 of
this file notmuch_database_add_message and helper functions not used
by any other function. This commit isolates this code into it's own
file.
Some side effects of this refactoring:
- find_doc_ids becomes the non-static (but still private)
_notmuch_database_find_doc_ids
- a few instances of 'string' have 'std::' prepended, avoiding the
need for 'using namespace std;' in the new file.
