assignment_collection._SymbolGenerator: Potential for generating non-unique symbols

>>> from sumpy.assignment_collection import _SymbolGenerator
>>> sg = _SymbolGenerator(set())
>>> sg("s_0")
s_0
>>> sg("s")
s
>>> sg("s")
s_0

mentioned in issue loopy#25 (closed)

mentioned in commit 573f110a

mentioned in merge request !27 (merged)

closed via commit 573f110a

closed via commit 6301c15a

mentioned in commit 6301c15a

mentioned in commit cc33b7d3