Throwing a more descriptive warning when reading a bad .gitignore

[john-science]

This is in response to the ticket: #2359

A particularly unhelpful error was thrown before, I feel this will be a lot more helpful to users trying to understand what went wrong.

[john-science]

I tried different .gitignore errors and found a few possible things that can go wrong, so I grabbed all three error types.

I also converted the error to SyntaxError. This is the only questionable choice I think I made in this tiny PR. I think it makes it more clear to the user; it is a gitignore syntax problem, after all.

[JelleZijlstra]

#2414 is already open trying to improve the same area.

[ichard26]

Sorry @john-science but we've decided that #2414 is a better fit for resolving this issue mostly since it hides away all of the scary traceback and exception messaging and replaces it with a clear error message. Thanks for the contribution and effort tho!

[john-science]

Sorry @john-science but we've decided that #2414 is a better fit...

No worries! Have a great weekend!