[notmuch] [PATCH] Mac OS X compatibility fixes

[Jeffrey C. Ollie]

Here's a patch that adds private implementations of strndup and
getline.  They are unconditionally compiled so that compiler errors in
these functions can be detected on any platform, even those that
provide strndup and getline in the standard library.  I'll have a
patch that handles the strndup/getline detection later today (I've
already done it in SCons, just need to figure out how I want to do it
in plain shell for the current configure script).