change log updates
doc: describing how to specify perl installation names.
properly resolve specified installation names.
doc: more description about `exec --with`
bump version number.
Merge branch 'release/0.46' into develop
Suppress warning about setting $MANPATH

When you have set $MANPATH manualy, calling manpath in .bashrc will
print a warning when starting a terminal session. Calling manpath with
the -q option will suppress this warning.
Merge pull request #223 from FreekKalter/develop

Suppress warning about setting $MANPATH
Small here-doc tweak.
Implement a "download" command.
fix test errors.
a sub routine that converts perl verion strings to an integer.
relocatable by default.
fix the test when there are intereferences..
fix the issue that PATH and PERL5LIB are written as constant in ~/.perlbrew/init
rewrite a few "http_get" to "download".
change log updates.
0.47
version bump.
document for the "download" command.