Finish the work started by Daniel in 2012, by using abstract local
AF_UNIX sockets on platforms that support them (Linux, Android).
Fix all sorts of bugs and issues that prevented the existing MDP and
Monitor client and server code from working with abstract socket names.
The new header "os.h" defines a supplemental API around existing basic
operating system services (system calls and standard library functions).
Moved some function prototypes from serval.h and net.h into os.h.
This allows non-servald executables to take advantage of this API without
having to include serval.h and bringing in all the other servald link-time
baggage.
Introduce __WHENCE__ macro and a block comment in log.h explaining it.
In "primitive" kinds of functions, rename 'whence' arguments to '__whence' and
use WHYF(), WARNF(), DEBUGF() macros instead of calling logMessage() directly.
Replaces (const char *file, unsigned int line, const char *function) arguments
to all logging functions, simplifies malloc/free tracking code in
overlay_buffer.c and Rhizome manifest alloc/free tracking in rhizome_bundle.c.
Use __HERE__ macro instead of (__FILE__, __LINE__, __FUNCTION__) everywhere.
Special __NOWHERE__ macro is equivalent to (NULL, 0, NULL).
Declare net.c functions in new "net.h" header, so log.c doesn't have to pull
in the entire "serval.h" just to use write_str().
Facilitates progress on issue #2.
Now write_str(), write_nonblock(), write_all(), set_nonblock() etc. report the
file/line/function of their caller, rather than the function in net.c. Done
using macros, similar in style to WHY() etc.
SET_NONBLOCKING(), SET_BLOCKING(), WRITE_STR() are now set_nonblock(),
set_block() and write_str() respectively, all of which log an error before
returning -1. There are other useful methods: write_all() treats anything less
than all bytes written as an error; write_nonblock() treats EAGAIN and EINTR as
zero bytes written, and a combination: write_all_nonblock().
