http: restore header folding behavior

Folded header lines will now get passed through like before. The headers
API is adapted and will provide the content unfolded.

Added test 1274 and extended test 1940 to verify.

Reported-by: Petr Pisar
Fixes #8844
Closes #8899

tests/data/test1940

@@ -12,6 +12,9 @@ HTTP/1.1 200 OK
 Date: Thu, 09 Nov 2010 14:49:00 GMT
 Server:       test with trailing space     
 Content-Type: text/html
+Fold: is
+ folding a     
+   line
 Content-Length: 0
 Set-Cookie: onecookie=data;
 Set-Cookie: secondcookie=2data;
@@ -44,7 +47,7 @@ http://%HOSTIP:%HTTPPORT/%TESTNUMBER
 
 # Verify data after the test has been "shot"
 <verify>
-<stdout>
+<stdout mode="text">
  Date == Thu, 09 Nov 2010 14:49:00 GMT
  Server == test with trailing space
  Content-Type == text/html
@@ -53,6 +56,7 @@ http://%HOSTIP:%HTTPPORT/%TESTNUMBER
 - Set-Cookie == onecookie=data; (0/3)
 - Set-Cookie == secondcookie=2data; (1/3)
 - Set-Cookie == cookie3=data3; (2/3)
+ Fold == is folding a line
 </stdout>
 </verify>
 </testcase>