bzip2: have two separate "store bit 0" and "store bit 1" functions

bzip2: have two separate "store bit 0" and "store bit 1" functions

function                                             old     new   delta
sendMTFValues                                       2051    2085     +34
bsW1_0                                                 -      33     +33
BZ2_compressBlock                                    225     223      -2
bsW1                                                  52       -     -52
------------------------------------------------------------------------------
(add/remove: 1/1 grow/shrink: 1/1 up/down: 67/-54)             Total: 13 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>