libc/uClibc: fix downloading pregen locales

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>
(transplanted from 223aaf040327e204f0801549e9c0cf6225bdf29d)

libc/uClibc: fix downloading pregen locales

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

scripts: in case of failed download, remove partial files

It happens from time to time that the server mis-behaves, and breaks the
connection right in the middle of nowhere, for no good reason, leaving us
with a partial file, on which the extract pass would choke.

Remove partial downloads, to fail early.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

scripts: when downloading, use aria2 only when //

Even when // downloads are not enabled, aria2 can
fail on some servers (eg. uclibc.org).

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

scripts: do not download in // by default

Parallel downloads can be a bit harsh on the servers,
and some will fail (eg. uclibc.org) in some cases.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

docs: move the Mercurial tutorial to the tutorials section

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

docs: split into multiple files

The overview.txt file has evolved into more than just an overview.
Split it into chapters, and include the misc tutorials.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>