printf integer format compatibility

[John W. Eaton]

While looking at some problems with printing 64-bit integer values with 
printf, I found that Matlab's printf function silently switches from 
integer formats like '%d' or '%u' to '%e' when values are not integers 
or when they exceed the maximum value possible for a 64-bit integer 
type.  Matlab also seems to be ignoring size specifications for integer 
formats, so although formats like '%hd' (short int) are accepted, there 
seems to be no change in output compared to just using '%d'.  And '%d' 
always handles up to 64-bit integers without needing 'l' or 'll'.

I checked in the following change on the default branch:

  http://hg.savannah.gnu.org/hgweb/octave/rev/491b0adfec95

Now you can expect behavior like the following, which appears to be 
compatible with Matlab:

  sprintf('%d',intmin('int32'))    %% ans = -2147483648
  sprintf('%d',intmax('int32'))    %% ans = 2147483647
  sprintf('%d',intmin('int64'))    %% ans = -9223372036854775808
  sprintf('%d',intmax('int64'))    %% ans = 9223372036854775807
  sprintf('%d',intmin('uint32'))   %% ans = 0
  sprintf('%d',intmax('uint32'))   %% ans = 4294967295
  sprintf('%d',intmin('uint64'))   %% ans = 0
  sprintf('%d',intmax('uint64'))   %% ans = 1.84467e+19
  sprintf('%d',realmin('single'))  %% ans = 1.17549e-38
  sprintf('%d',realmax('single'))  %% ans = 3.40282e+38
  sprintf('%d',realmin('double'))  %% ans = 2.22507e-308
  sprintf('%d',realmax('double'))  %% ans = 1.79769e+308

There is still one difference:  Matlab switches to '%e' and Octave is 
currently switching to '%g'.  Should we follow Matlab exactly here?  I 
generally prefer '%g' over '%e' because it seems easier to me to read 
numbers without unnecessary e+04 style exponents appended.

This change caused a few new test failures in cases where '%d' was 
previously assumed to always produce an integer result.  I fixed one 
problem in the datestr function by rounding the printf argument that was 
used with a '%d' format.  I could use some help fixing the stemleaf 
function since I'm not sure what the intent is there.

jwe