bioinfo: still messing around with table typing
various fixes for mouse ES example
bioinfo/bowtie: fixed symlink from index to genome sequence

bowtie-index pipeline would add a symlink to the fasta sequence just
next to the index, so that bowtie doesn't have to reconstruct it
before aligning. However this is a bug, as the fasta pipeline might be
deleted in the cache, which breaks the symlink. The current fix is to
copy the fasta file instead of symlinking it but maybe that's not
worth it?
guizmin.console: improved cache selection API

now labels can be counted for a period not finishing now.
guizmin_table: richer typing of file formats

the type ['a Guizmin_table.format] is now reacher as it indicates the
possible presence of comments and header in addition to the format of
a row. This enabled the static detection of a bug in test_mouse_ES,
namely that you can't use macs xls output as bed files.

Note that the functions to read tables in [Guizmin_table] are not yet
able to ignore comments.
guizmin_table: pipeline to remove comments and headers