Make .o files in separate subdirectories for servald and library
Factor struct __sourceloc and __WHENCE__ from "log.h" into "whence.h"
Factor sid_t etc from "serval.h" into "serval_types.h"
Factor rhizome_bid_t etc from "rhizome.h" into "rhizome_types.h"
Do not include "serval.h" in library sources
Add log_stderr.c and logMessage.c for stand-alone executables
So that "http_server.h" does not have to include "serval.h" which
creates a circular dependency.
Remove the __SERVALDNA__HTTP_SERVER_IMPLEMENTATION hack from
"http_server.h"
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.
Add str.h to list of Serval header files. Make the NaCl objects not dependent
on Serval header files, so that the entire NaCl source does not get re-built
when editing serval.h or str.h etc.
