Fixing a few edge cases while shuffling

[wongjingping]

Fixing a few edge cases while shuffling.
The main error here is how the section before the comment (if present) could contain more than 1 comma (eg ytd_return numeric(10,2),), and if we just check for trailing commas using "," in col that would give false positives in the following case:

col = "  ytd_return numeric(10,2)"
"," in col
# returns True but there is no trailing comma!

Also added tests for fix_comma since that's where the comma fixing happens.

[rishsriv]

Aaaah GREAT find! Thanks for the fix :D