Get rid of calc_bc_dist_func, the only times this was used was when

Get rid of calc_bc_dist_func, the only times this was used was when
yasm_common_calc_bc_dist was used.  Rename yasm_common_calc_bc_dist to
yasm_calc_bc_dist, call it directly from the expr functions, and change
higher-level callers to boolean flags of whether to calculate bc distance
or not.

svn path=/branches/new-optimizer/; revision=1550