sync
fix some crashes in orc by not freeing orc stuff

a leak is better than a crash :( or build vips without orc if you don't
want a leak either

lots of stuff along the lines of:

==13114== Invalid write of size 8
==13114==    at 0xB81B229: orc_code_chunk_merge (orccodemem.c:107)
==13114==    by 0xB82B13D: orc_code_free (orccode.c:33)
==13114==    by 0xB81B89A: orc_program_free (orcprogram.c:175)
==13114==    by 0x6508AA4: vips_vector_free (vector.c:106)