This fix a problem with the garbage collector not being able to
clean the MetaElements that are loaded.

On small projects this is not a problem, but in bigger projects, this
can save a few hundred of MBs at runtime

The reason behind this is, whenever we have a "stack" element, which
has no stack.yaml configuration, since it doesn't need it, we would
get an exception thrown when initiating the first one, as loading the
yaml file would fail.

This would capture the frame in which this command was executed, which
references meta_elements. Therefore, as long as another exception is not
thrown, the garbage collector would not be able to clean all the
MetaElements.

Cleanup MetaElement local state

See merge request !1147

Chandan Singh authored Feb 13, 2019 and Chandan Singh committed Feb 13, 2019

This script leverages the recently added format strings
(`%{build-deps}`, `%{runtime-deps}`) to `bst show` to print a graph in
DOT format. This requires users to have the `graphviz` python package
installed.

Additionally, users can also render the graph using the `--format`
option if they have the `graphviz` command line tool installed.