When tracking down some potential issues in the nginx constellation,
we've found it useful to understand where particular error messages
are coming from, since many of the same messages are repeated in
various places. This patch will write the source file from which the
message originated, the function name, and the line number if you're
using GCC to compile nginx. Here's an example:

Old Output:
2010/01/12 14:43:10 [notice] 67772#0: nginx/0.7.64
2010/01/12 14:43:10 [notice] 67772#0: built by gcc 4.0.1 (Apple Inc. build 5490)
2010/01/12 14:43:10 [notice] 67772#0: OS: Darwin 9.8.0
2010/01/12 14:43:10 [notice] 67772#0: hw.ncpu: 2
2010/01/12 14:43:10 [notice] 67772#0: net.inet.tcp.sendspace: 65536
2010/01/12 14:43:10 [notice] 67772#0: kern.ipc.somaxconn: 128
2010/01/12 14:43:10 [notice] 67772#0: getrlimit(RLIMIT_NOFILE):
256:9223372036854775807
2010/01/12 14:43:10 [notice] 67772#0: start worker processes
2010/01/12 14:43:10 [notice] 67772#0: start worker process 67785
2010/01/12 14:43:16 [notice] 67772#0: signal 20 (SIGCHLD) received

New Output:
2010/01/14 16:35:09 [notice] 27241#0: src/os/unix/ngx_posix_init.c
ngx_os_status(   80) nginx/0.7.64
2010/01/14 16:35:09 [notice] 27241#0: src/os/unix/ngx_posix_init.c
ngx_os_status(   83) built by gcc 4.0.1 (Apple Inc. build 5490)
2010/01/14 16:35:09 [notice] 27241#0: src/os/unix/ngx_darwin_init.c
ngx_os_specific_status(  153) OS: Darwin 9.8.0
2010/01/14 16:35:09 [notice] 27241#0: src/os/unix/ngx_darwin_init.c
ngx_os_specific_status(  166) hw.ncpu: 2
2010/01/14 16:35:09 [notice] 27241#0: src/os/unix/ngx_darwin_init.c
ngx_os_specific_status(  166) net.inet.tcp.sendspace: 65536
2010/01/14 16:35:09 [notice] 27241#0: src/os/unix/ngx_darwin_init.c
ngx_os_specific_status(  166) kern.ipc.somaxconn: 128
2010/01/14 16:35:09 [notice] 27241#0: src/os/unix/ngx_posix_init.c
ngx_os_status(   92) getrlimit(RLIMIT_NOFILE):
2560:9223372036854775807
2010/01/14 16:35:09 [notice] 27241#0: src/os/unix/ngx_process_cycle.c
ngx_start_worker_processes(  337) start worker processes
2010/01/14 16:35:09 [notice] 27241#0: src/os/unix/ngx_process.c
ngx_spawn_process(  201) start worker process 27254
2010/01/14 16:35:14 [notice] 27241#0: src/os/unix/ngx_process.c
ngx_signal_handler(  420) signal 20 (SIGCHLD) received

Formatting the filename and function name fields into fixed-width
fields would be nicer, however that would require further changes in
src/core/ngx_string.c

(C) Brian Moran - bmoran@onehub.com  (posted to nginx-devel mailing list on 15/01/10)
