add thread count to linux_proc

[Stan Cox <scox@xxxxxxxxxx>]

This adds VmSwap and Threads to linux_proc as proc.memory.vmswap and 
proc.psinfo.threads.
pmdas/linux_proc.c looks at /proc/NN/status in the order:
 VmSize, VmLck, VmRss, VmData, VmStk, VmExe, VmLib
but on more recent kernels the order is:
 VmSize, VmLck, VmPin, VmHWM, VmRss, VmData, VmStk, VmExe, VmLib
so the patch also allows for skipping those if required.

Testing via dbpmda:
dbpmda -n root | awk '/^ *inst/ {if ($2=="[32151") print $0;next} /> 
desc/ {printf "%s: ",$3} /PMID:/ {print $0} /> fetch/ {printf "fetch 
%s:",$3}'
proc.memory.vmsize: PMID: 3.24.20
proc.memory.vmlock: PMID: 3.24.21
proc.memory.vmrss: PMID: 3.24.22
proc.memory.vmdata: PMID: 3.24.23
proc.memory.vmstack: PMID: 3.24.24
proc.memory.vmexe: PMID: 3.24.25
proc.memory.vmlib: PMID: 3.24.26
proc.memory.vmswap: PMID: 3.24.27
proc.psinfo.threads: PMID: 3.24.28
fetch proc.memory.vmlib:    inst [32151 or ???] value 70620 
9.8959698e-41 0x113dc
fetch proc.memory.vmswap:    inst [32151 or ???] value 0 0 0x0
fetch proc.psinfo.threads:    inst [32151 or ???] value 332 
4.6523109e-43 0x14c
Double checking /proc/32151/status:
egrep 'VmLib|VmSwap|Threads' /proc/32151/status
VmLib:     70620 kB
VmSwap:        0 kB
Threads:        332

linux_proc.diff
Description: Text Data