data already accumulated in the buffer (i. no less than the value of TBuffer::Length()).

In TBranch::SetBasketSize, instead of using the hard minimum of 100, use
100 + the length of the branch name (as 100 is too smalli to hold the 
basket's key information for any branch name larger than 30 characters).

This fixes the write past the end of buffer (leading to segfaults)
reported in Savannah:  <http://savannah.cern.ch/bugs/?89645>


git-svn-id: http://root.cern.ch/svn/root/trunk@42423 27541ba8-7e3a-0410-8455-c3a389f83636