dc: tweak parsing

dc: tweak parsing

https://bugs.debian.org/538685
dc requires whitespace between language elements.

We were requiring
1 2 + p
instead of the abbreviated
1 2+p
(for example).

function                                             old     new   delta
stack_machine                                         97     126     +29
dc_main                                              117      79     -38
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 1/1 up/down: 29/-38)             Total: -9 bytes

Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>