Fix 199468 - Suppressions: stack size limited to 25 while --num-callers allows more...

Fix 199468 - Suppressions: stack size limited to 25 while --num-callers allows more frames

Nr of callers in a suppression entry had a smaller limit than the max
for --num-callers.
This means it was not possible to precisely suppress an error with a big
stack trace.
Also, --gen-suppressions was not providing the full stack trace of
the error in the generated suppressions.

Now, a suppression entry can have the same nr of callers as a backtrace.
Generated suppressions are generated with up to --num-callers callers.

This change has neglectible impact :
* memory: stack array of 500*2 words is declared, instead of 24*2 words
  This array is declared on the interim stack (startup stack), which is
  largely big enough.
* cpu : neglectible more cpu needed to read suppression entries
        (to initialise the bigger stack array when reading a supp entry),
Apart of the above, no impact on performance (unless of course bigger
supp entries are really used).

Note that this does not impact the behaviour for existing suppression files.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@15945