Enable io stats only for linux

Code currently only supports linux for reporting i/o stats.
- fix build on mips64
catch up with change KERN_PROC2 -> KERN_PROC
sync with top(1) in base; remove KERNBASE. ok okan@
Add ignore file
Current query only for linux

Disable the mode toggling for getting the current query until it can be
implemented on platforms other than linux.
Fix library searching in configure

Set the LDFLAGS with the library search path for postgres library.