[PATCH 0/4] External 'filter' attributes and drivers

I know this is controversial, but here is a small four patch series to let you insert arbitrary external filter in checkin and checkout codepath.

[PATCH 1/4] Simplify calling of CR/LF conversion routines [PATCH 2/4] convert.c: restructure the attribute checking part. [PATCH 3/4] lockfile: record the primary process. [PATCH 4/4] Add 'filter' attribute and external filter driver definition.

[1/4] is Alex's earlier patch, rebased on top of 'next'.

[3/4] is necessary for the series because otherwise 'git add' would not work with any external filter, but the change is applicable to 'master'.

[4/4] is the body of the change. I wanted to like run-command.h process spawning infrastructure, but I suspect I did not use it optimally. People who were more involved in its evolution hopefully have suggestions for better use of it.