find_column_option_info: drop unused variable

This was introduced by 271fd86 (Refactor view column option
lookup to make it reusable, 2014-11-08), but is not used.
parse_view_settings: drop unused variables

These were made redundant by caea679 (Cleanup view settings
parsing, 2014-11-09).
parse_view_config: drop unused variables

These were obsoleted when the loop logic was factored out in
25795d3 (Make parsing of view column expressions reusable,
2014-11-09).
parse_view_column_config: drop unused variables

These were introduced with the function in 2670414 (Add
shorthand for changing the view settings of a single column,
2014-11-09), and never used.
parse_view_column_config: avoid reading uninitialized/NULL variable

If the view does not support a specific type or we cannot
find a matching column, we do not want to use "column->type"
to report the error. It is either uninitialized or NULL in
these error conditions. Instead, we can want to use the type
we are looking for.
Add test for using view column short hand for unconfigured columns
Ensure default build options include -Wall even on Mac OS X

This should help this poor guy to avoid leaving behind a mess of unused
variables. It also makes it easier to override OS-based config
variables.