Major stuff:
- Created a FileCache for managing user cache files in Spack. Currently just
handles virtuals.
- Moved virtual cache from the repository to the home directory so that users do
not need write access to Spack repositories to use them.
- Refactored `Transaction` class in `database.py` -- moved it to
`LockTransaction` in `lock.py` and made it reusable by other classes.
Other additions:
- Added tests for file cache and transactions.
- Added a few more tests for database
- Fixed bug in DB where writes could happen even if exceptions were raised
during a transaction.
- `spack uninstall` now attempts to repair the database when it discovers that a
prefix doesn't exist but a DB record does.
- Spack will check if the index needs updating, and will only parse
all package files if it does.
- Spack tries to parse as few package files as necessary.
- Don't need to list all packages unless we have to.
- Only use the list of all packages for existence checks if we have
generated it for some other purpose.
This PR will catch the error where the url can not be determined from a
VCS URL, such as git. It will print a message to the console and move on
because it should not be a fatal error at this point in the process.
This should fix#1459.
The archive_version variable should only get set if versions will be
checked and that is only if there is a list_url in the package file. For
VCS repos setting the variable triggers an error from web.py as it
parses the default_fetcher object.
This should fix#1422.
Assuming a bash interactive environment will be correctly formed on login, we
should prefer to probe the environment using a shell that reports itself as
`bash` instead of `sh` which may not source files that set the
environment modules in statements like:
```
case "$is" in
bash) test -s /etc/bash.bashrc.local && . /etc/bash.bashrc.local ;;
ksh) test -s /etc/ksh.kshrc.local && . /etc/ksh.kshrc.local ;;
zsh) test -s /etc/zsh.zshrc.local && . /etc/zsh.zshrc.local ;;
ash) test -s /etc/ash.ashrc.local && . /etc/ash.ashrc.local
esac
test -s /etc/sh.shrc.local && . /etc/sh.shrc.local
```
