Make source package: Use a custom dialog with a "fool GMail" explicit option....

Make source package: Use a custom dialog with a "fool GMail" explicit option. Some fixes in the project property dialog environment tab.

[DEVELOPMENT ENVIRONMENT]
* NEW: Make source package: Use a custom dialog with a "fool GMail" explicit option.
* NEW: Project property dialog: The variable name column of the environment grid now enlarges itself when inserting a new variable.
* BUG: Project property dialog: Fix a possible crash when closing the dialog.