mq: strip extra whitespace from node ids in header (
issue2790)
This makes `hg qpush --exact` work with patches created by `hg export`.
prevent transient leaks of file handle by using new helper functions
These leaks may occur in environments that don't employ a reference
counting GC, i.e. PyPy.
This implies:
- changing opener(...).read() calls to opener.read(...)
- changing opener(...).write() calls to opener.write(...)
- changing open(...).read(...) to util.readfile(...)
- changing open(...).write(...) to util.writefile(...)