Improve error: literal notation of illegal symbolic values

[helins]

No useful error message is provided when an illegal symbolic value is evaluated:

:42

;; READER: Reader error: Parse error at Position{line=1, column=2} Source: <4> Message: null

'#42/24

;; READER: Reader error: Parse error at Position{line=1, column=6} Source: <2> Message: null

[helins]

Behaves weirdly since ANTLR move. Eg. :4 returns nil, :42 returns 2.

[mikera]

Parser error handling issue (handling of invalid symbols etc.)