calc: sort+headers: don't use GNU sed.

Implement unbuffered input to avoid GNU sed dependency.
calc: bugfix on --sort without grouping.

'pipe_through_sort' was not cleared, caused errors on FreeBSD
(all other systems seems not to mind calling pclose on a non-popen
FILE).
TravisCI - no need for GNU Sed 4.2.2 anymore.
RENAME: calc -> compute

To avoid name conflicts with existing software.
build: update helper scripts to new name
maint: add helper script to upload files to AWS S3
packaging: update Debian files after name change
Merge branch 'master' into debian/unstable