Pull in dependencies of strictness=3 MatchSpec's

[whitequark]

Before this change, MatchSpec's (i.e. package dependencies) of
strictness=3 (i.e. with an equality constraint on all of name, version
and build) did not bring the dependencies of the packages they
depend on into consideration, which resulted in assertion failures.

For example, let's consider three packages:

host-plugin/meta.yaml:

package:
  name: host-plugin
  version: {{ environ.get("GIT_DESCRIBE_TAG", "") }}
build:
  string: {{ environ.get("GIT_DESCRIBE_HASH", "") }}
requirements:
  build:
    - host
  run:
    - host {{ "{tag} {hash}".format(
                  tag=environ.get("GIT_DESCRIBE_TAG"), 
                  hash=environ.get("GIT_DESCRIBE_HASH")) 
                if "GIT_DESCRIBE_TAG" in environ else "" }}

host/meta.yaml:

package:
  name: host
  version: {{ environ.get("GIT_DESCRIBE_TAG", "") }}
build:
  string: {{ environ.get("GIT_DESCRIBE_HASH", "") }}
requirements:
  run:
    - dep

dep/meta.yaml:

package:
  name: dep
...

This results in the following failure while trying to install
host-plugin:

  File "~/.miniconda/lib/python3.4/site-packages/conda/resolve.py", line 624, in gen_clauses
    assert len(clause) > 1, '%s %r' % (fn1, ms)
AssertionError: host-plugin-0.0-g123456.tar.bz2 MatchSpec('dep')

After this change, the installation succeeds.

[whitequark]

One test fails. I do not have an understanding of conda deep enough to recognize the impact of that failure.

[rekcahpassyla]

Looks like #1766 is the fix for this?

[whitequark]

Right.

[github-actions]

Hi there, thank you for your contribution to Conda!

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