gcc 4.6 -Wunused-but-set-variable

Another set of new gcc 4.6 warnings:

readfuncs.c: In function ‘_readCaseWhen’:
readfuncs.c:875:567: warning: variable ‘token’ set but not used [-Wunused-but-set-variable]
readfuncs.c: In function ‘_readFromExpr’:
readfuncs.c:1159:568: warning: variable ‘token’ set but not used [-Wunused-but-set-variable]

read.c: In function ‘nodeTokenType’:
read.c:222:8: warning: variable ‘val’ set but not used [-Wunused-but-set-variable]

I couldn't see a way good way of programming around this (perhaps in the
second case, but it would get uselessly ugly), so perhaps just marking
the variables as potentially unused would be appropriate?  See patch.