Re: Cleanup shadows variable warnings, round 1

0001 - simple cases of local variable shadowing local variable by changing inner variable to for loop variable (also need to rename the for loop var)

0002 - simple cases of local variable shadowing local variable by renaming  inner variable 

0003 - simple cases of local variable shadowing local variable by renaming outer variable. In this commit, outer local variables are used much less than inner variables, thus renaming outer is simpler than renaming inner.

0004 -  still local shadows local, but caused by a macro definition, only in inval.c

0005 - cases of global wal_level and wal_segment_size shadow local ones, fixed by renaming local variables

0006 - in xlogrecovery.c, some static file-scope variables shadow local variables, fixed by renaming local variables

0007 - cases of global progname shadows local, fixed by renaming local to myprogname

0008 - in file_ops.c, some static file-scope variables shadow local, fixed by renaming local variables

0009 - simple cases of local variables are shadowed by global, fixed by renaming local variables

0010 - a few more cases of static file-scope variables shadow local variables, fixed by renaming local variables

0011 - cases of global conn shadows local variables, fixed by renaming local conn to myconn

0012 - fixed shadowing in ecpg.header

0013 - fixed shadowing in all time-related modules. Heikki had a concern where there is a global named “days”, so there could be some discussions for this commit. For now, I just renamed local variables to avoid shadowing.