library: refactor and rely on modern kernels for wchan

Several Debian based distributions were recently found
to have omitted a kernel configuration option that had
the effect of rendering /proc/#/stat and /proc/#/wchan
useless for providing any 'sleeping in function' info.

That problem also prompted a reevaluation of the whole
approach to wchan matters which had grown increasingly
complex as our library evolved over the last 13 years.

The net result was a decision to rely on /proc/#/wchan
which arrived along with the 2.5 kernel. This then let
us vastly simplify the internal code plus the external
interface which will benefit both the top and ps pgms.

Reference(s):
http://www.freelists.org/post/procps/WCHAN,11
https://lkml.org/lkml/2008/11/6/12
https://bugs.debian.org/711592

Signed-off-by: Jim Warner <james.warner@comcast.net>

proc/wchan.h

@@ -5,9 +5,7 @@
 
 EXTERN_C_BEGIN
 
-extern const char * lookup_wchan(unsigned KLONG address, unsigned pid);
-extern int   open_psdb(const char *__restrict override);
-extern int   open_psdb_message(const char *__restrict override, message_fn message);
+extern const char * lookup_wchan (int pid);
 
 EXTERN_C_END