parsers: fix uninitialize variable warning The heads pointer is not initialized correctly if filter is false, causing both clang and gcc to issue a warning. Correctly initialize heads to NULL.

revset: use `subset &` in bare `p2()` This takes advantage of the `fullreposet` smartness with a nice speedup. It's a similar speedup to `p1()` when a merge is in progress (the non merge case is already lightning fast anyway.)

revset: use `subset &` in bare `p1()` This takes advantage of the `fullreposet` smartness and yields a nice speedup. revset #0: p1() 0) wall 0.003256 comb 0.010000 user 0.010000 sys 0.000000 (best of 527) 1) wall 0.000066 comb 0.000000 user 0.000000 sys 0.000000 (best of 23224)

revset: use `subset &` in `rev` This takes advantage of the `fullreposet` smartness and yields a nice speedup. revset #0: rev(25) 0) wall 0.005480 comb 0.000000 user 0.000000 sys 0.000000 (best of 305) 1) wall 0.000052 comb 0.000000 user 0.000000 sys 0.000000 (best of 21891)

revset: use `subset &` in `origin` This takes advantage of the `fullreposet` smartness. revset #0: origin(tip) 0) wall 0.005353 comb 0.000000 user 0.000000 sys 0.000000 (best of 354) 1) wall 0.003080 comb 0.000000 user 0.000000 sys 0.000000 (best of 446)

revset: use `subset &` in `follow` This takes advantage of the `fullreposet` smartness. revset #0: follow(COPYING) 0) wall 0.002446 comb 0.000000 user 0.000000 sys 0.000000 (best of 735) 1) wall 0.000331 comb 0.000000 user 0.000000 sys 0.000000 (best of 5672)

revset: use `subset &` in `filelog` This takes advantage of the `fullreposet` smartness. revset #0: file(COPYING) 0) wall 3.179066 comb 3.180000 user 3.140000 sys 0.040000 (best of 3) 1) wall 2.723699 comb 2.730000 user 2.690000 sys 0.040000 (best of 4)