fix v71.vtc again for systems with smaller pointers
fix v71.vtc again for systems with smaller pointers

beeaa19cced3fe1ab79381b2b1b7b0b5594cbb18 had left 32 bytes on the client
workspace for the /baz case, which was sufficient to write resp.http.x-of
for 4-byte alignment, but not 8byte alignment:

* "false\0"		=  6b
* "x-of: false\0"	= 12b

gquintard/Varnish-Cache,gquintard/Varnish-Cache,gquintard/Varnish-Cache,gquintard/Varnish-Cache