Hello,

This finishes the mi1/mi2/mi3 rollover.  It also fixes a bug.  The 
previous changes forgot to register "mi2", and set "mi" to "mi3". 
Anyway it:

- adds "mi2" and "mi3"
- makes "mi" select "mi2" the last released "mi" version.
- updates the doco to mention that "mi2" was released in GDB 6.0
- rolls the testsuite so that there is a frozen mi2-*.exp

Note that "mi" is selecting "mi2" the last released version, and not the 
next version.  This gives better consistency between the last branch and 
the current release - "mi" should select the same thing - and that might 
encourage people to pick up current snaps.

I expect adding this to 6.0 and mainline in a few days.

I should note that I'm not sure how consistent my rollover process is - 
I suspect last time "mi" ended up selecting the mainline, instead of the 
previous released version.  I guess, given miN as the default, the 
process is:

Freeze an MI version (on the branch):
- delete mi{N-1}
- make "mi" select mi{N+1}
- copy mi{N+1}-*.exp to mi-*.exp, s/-i=mi{N+1}/-i=mi/

Start a new MI version (on the mainline):
- add mi{N+2}
- copy mi{N+1)-*.exp to mi{N+2}-*.exp, s/-i=mi{N+1}/-i=mi{N+2}/

thoughts?
Andrew