DOC: fix bogus recommendation on usage of gpc0 counter

The doc pretends that src_inc_gpc0 may be used alone without an integer
match, but this is false and has always been since its introduction in
1.5-dev1. If the ACL is called, the increment will be used, the value
returned, but it will be matched against no value so the resulting ACL
will never be true and the condition will not be met.

This means that the following config :

     acl abuser src -f abusers.lst
     acl blacklist src_inc_gpc0
     tcp-request connection reject if abuser blacklist

Will never reject the connection and must be fixed this way :

     acl abuser src -f abusers.lst
     acl blacklist src_inc_gpc0 gt 0
     tcp-request connection reject if abuser blacklist

Note that clr_gpc0 is trickier, as it returns the previous value which
might also be zero. Thus it's suggested to compare it against any positive
value including zero :

     tcp-request connection accept if { src_clr_gpc0 ge 0 }

Some arguments were missing on the sc1/sc2 forms of most ACLs including
gpc0, so this has been fixed too.
BUG/MINOR: http-compression: lookup Cache-Control in the response, not the request

As stated in both RFC2616 and the http-bis drafts, Cache-Control:
no-transform must be looked up in the response since we're modifying
the response. However, its presence in the request is irrelevant to
any changes in the response :

  7.2.1.6. no-transform
   The "no-transform" request directive indicates that an intermediary
   (whether or not it implements a cache) MUST NOT change the Content-
   Encoding, Content-Range or Content-Type request header fields, nor
   the request representation.

  7.2.2.9. no-transform
   The "no-transform" response directive indicates that an intermediary
   (regardless of whether it implements a cache) MUST NOT change the
   Content-Encoding, Content-Range or Content-Type response header
   fields, nor the response representation.

Note: according to the specs, we're supposed to emit the following
response header :

  Warning: 214 transformation applied

However no other product seems to do it, so the effect on user agents
is unclear.
DOC: typo and minor fixes in compression paragraph
MINOR: config: http-request configuration error message misses new keywords

"redirect" and "tarpit" keywords were missing from http-request configuration
error message.