external_acl parameters separated by %20 instead of space

external_acl parameters separated by %20 instead of space

If an external ACL is configured with more than one parameter as shown
in the example below, then Squid sends those parameters to the
external_acl helper separated by %20 characters instead of spaces:

  acl TEST external ACLTYPE param1=val1 param2=val2

This change fixes regression introduced in trunk r14351 (Support
logformat %macros in external_acl_type format) but more work may
be needed to make Squid behave as squid.conf.documented promises.

This is a Measurement Factory project.