Removing duplicate SQR macros.

This fixes all non-const related warnings in plugins/.
Make BC_FileBox::update_filter() use const argument.

This is needed to get rid of all warnings when building plugins.
Make PluginVClient::next_effect_is() and PluginVClient::prev_effect_is() use const argument.

This is needed to get rid of all warnings when building plugins.
Fix const related warnings in plugins/.
Correct formatting in BC_WindowBase::dispatch_event().

There is a print statement in BC_WindowBase::dispatch_event() trying
to print an XID cast to unsigned char using %lx.  This causes a
compiler warning, and probably will not result in the expected output.
This patch fixes the issue.
Removed unused EditPanel::delete_buttons
We use git now.