This originally use Xapian::Unicode::is_wordchar, but that forces
clients to link directly to libxapian, which seems like it might be
busywork if nothing else.
It turns out that our use of GMimeStreamPipe has only succeeded
because gmime has been ignoring some seek failures; this will no
longer be the case in gmime 3.0, so we use a GMimeStreamPipe, which
does not assume seekability, wrapped in a buffering stream.
Apparently some systems (MacOS?) have a system library called libutil
and the name conflict causes problems. Since this library is quite
notmuch specific, rename it to something less generic.
The idea is to provide a more or less drop in replacement for readline
to read from zlib/gzip streams. Take the opportunity to replace
malloc with talloc.
This is to give a home to strtok_len. It's a bit silly to add a header
for one routine, but it needs to be shared between several compilation
units (or at least that's the most natural design).
We keep the lib/xutil.c version. As a consequence, also factor out
_internal_error and associated macros. It might be overkill to make a
new file error_util.c for this, but _internal_error does not really
belong in database.cc.
