b=11048
r=brian

Fix infinite loop when used with newer bash version (3.1.17)

- b1_4 is basically the parent of HEAD, because that's the direction
  that changes flow, as strange as that sounds.  so there's a
  HEAD_BASE tag which sits on b1_4

b_cmobd_merge should not be used for any further development or testing!

cMD_PRE_CMD_SMASH are the relevant tags.

The pre-smashing contents of HEAD will be committed by yury into b_cmd as a
merge of the two branches.  These will be stabilized on b_cmd and eventually
landed onto HEAD.

the PATH, so I (and other users) don't have to remember where they are.

b=2912/2922, b=3145 too

b=3057, 2947, 2925, 3050, 3041, 2849, 1662

- remove extN/ files

with both 2.13 and 2.53.