Back porting coverity issues fix patch from master branch.
Fix coverity issue:1111377 Unchecked return value
Fix coverity issue:1111381 Logically dead code
Fix coverity issue:1222992 Unchecked return value
Fix coverity issue:1222993 Unchecked return value
Fix coverity issue:1222996 Printf arg type mismatch
Fix coverity issue:1222997 Printf arg type mismatch

For the coverity issue 1222996 and 1222997 the return type of NameListToString function
is changed from string* to char*, and defination of the which is the return type of the function in PostgreSQL source.
and appropriate changes have been made in the code to incorporate this function return type change.

For coverity issue:1222992 1222993 the return type of do_query() function is changed to void from POOL_STATUS.
The function’s return value became insignificant after the introduction of elog API,
After the API do_query() only returns in a successful scenarios and throws an ereport
in case of any error within the function.
Change pgpool_status file format to ASCII.

Changing to ASCII will bring some benefits:
- Easy to check the file contents by using ordinary text tools
- Easy to modify the contents. This is useful if you set longer health check time out.
  For example, newly added backend will cause failover and it might take long time
  until the procedure finishes. By editing pgpool_status to set the new node
  status as down, you could avoid health checking for the node.

Note that the new file reader understands old binary format
pgpool_status for easy migration from older versions of pgpool-II.
Fix for the segmentation fault, which was unearthed while testing. The crash only
exists in master branch, and was caused by import of memory manager.
The reason for the crash was check_copy_from_stdin() function was making the persistent copies
of copy_schema, copy_nulls and copy_table in wrong memory context, whose lifecycle
is shorter than the lifecycle of global variables (copy_schema, copy_nulls and copy_table).
This checkin fix the fault by replacing pstrdup() with
MemoryContextStrdup() and using TopMemoryContext.
Remove meaningless minus check because of unsigned int variable.

Coverity issue #1111419, #1111420, #1111422.