Allow \pset to parse "on or off" for boolean values - Mailing list pgsql-patches

This is a TODO item:

        o Allow psql \pset boolean variables to set to fixed values, rather
          than toggle


Basically allows for:
test=# \pset expanded on
Expanded display is on.
test=# \pset footer off
Default footer is off.
test=# \pset footer
Default footer is on.
test=# \pset footer
Default footer is off.
test=# \pset footer
Default footer is on.


Basically the change is to check if value in do_pset is != NULL to call ParseVariableBool to get a true/false and set the value directly, of the second parameter is not provided then the "old logic" of toggling is supported.

The pset variables that are adjusted are:
expanded
numericlocale
tuples_only
pager (supports on/off/always now)
footer