http: add --strip-path-slash and CURLOPT_STRIP_PATH_SLASH

... to enable sending "OPTIONS *" which wasn't possible previously.

This option currently only works for HTTP.

Added test cases 1298 + 1299 to verify

Fixes #1280
Closes #1462

include/curl/curl.h

@@ -1780,6 +1780,9 @@ typedef enum {
   /* Suppress proxy CONNECT response headers from user callbacks */
   CINIT(SUPPRESS_CONNECT_HEADERS, LONG, 265),
 
+  /* Strip the initial slash from the path taken from the URL */
+  CINIT(STRIP_PATH_SLASH, LONG, 266),
+
   CURLOPT_LASTENTRY /* the last unused */
 } CURLoption;