Extend the base used for the upload script.

The base used for the upload script contained only lower case letters
and digits.

This patch adds upper case letters which further reduce the name length
of the uploaded files.
upload: Improve the compression of upnames

Until now the upname compression concatenated two numbers in base 62. We
now change the base of one big number which save a few more bits of
information.
upload: Use the apparent size

When using the physical size, a lot of small files will have the same
size. That is, one disk block of 4096B. Hence the size component of the
upname was useless.

This patch uses the apparent size of the file instead.