Allow compile results to be merged

[delphidabbler]

At present when editing a snippet if a test compile is run the results obtained replace the pre-existing results.

It would be useful to have the option of merging the test results with pre-existing results instead of overwriting them. This will enable existing results from no longer available compilers to be preserved.

[delphidabbler]

This would only apply when test compiling user defined snippets from the snippets editor.