parseconfig: warn if unquoted white spaces are detected

parseconfig: warn if unquoted white spaces are detected

Commit 0db811b6 made some existing config files pass on unexpected
values to libcurl that made it somewhat hard to track down what was
really going on.

This code detects unquoted white spaces in the parameter when parsing a
config file as that would be one symptom and it is generally a bad
syntax anyway.