Bump octave version to 4.2.1

[jgillis]

Blocked by missing information.

As of octave version 4.2, the structure of the octave binaries changed for windows: there are now 2 flavours, using 32 and 64 prefixes.
It's not clear to me how these new downloads map to the 3 octave-crossbuild configurations documented at http://wiki.octave.org/Continuous_Build: w32-on-debian , w64-32-on-debian , w64-64-on-debian

Does the 32 prefixed download correspond to w32-on-debian or to w64-32-on-debian?

[jweaton]

The configuration for the buildbot builds is as follows:

w32: 32-bit Windows, so 32-bit pointers and limited to 32-bit indexing. You can only allocate up to about 4GB total memory because of the limit imposed by using 32-bit pointers. This is distributed as the w32 binary on ftp.gnu.org.

w64-32: 64-bit Windows, so 64-bit pointers, allowing larger memory allocation, but limited to 32-bit indexing in Octave. This allows arrays up to about 2^31 elements, so for a double precision array, that requires about 16GB of memory. This is distributed as the w64 binary on ftp.gnu.org.

w64-64: 64-bit Windows and 64-bit indexing. We're not distributing this one as a binary release.

[jgillis]

Bump finished