It turns out that putting inline functions in C header files is not a
good idea, and can cause linking problems if the compiler decides not
to inline them. In principle this is solvable by using a "static
inline" declaration, but this potentially makes a copy in every
compilation unit. Since we don't actually care about the performance
of this function, just use a non-inline function.
libnotmuch_util.a is supposed to be usable from the library and the
CLI, but much the library is compiled as C++. Add in appropriate
wrapping to prevent symbol mangling. These wrappers already existed in
string-util.h; it seems better to be consistent.
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.
