Fix ClassMapGenerator unambiguousReference test coverage

Without this fix the test only covers having files in "test", the "fixture"
portion it is not covered at all, because all fixtures in phpunit tests
are already in "test" directory
Avoid ambiguity warning for example directories as well

In particular, PEAR repositories use a classmap and example directories trigger
multiple false positive warnings.
Merge pull request #2895 from SlikNL/classmap-warning-example

Improve ambiguity warning test coverage and avoid ambiguity warning for example directories
Fix removal of missing keys
Fix some more inconsistencies in json manipulation
Removing dist reference info from Artifact Repository

The getComposerInformation method adds dist information to package. This includes reference, which holds the name of the zip file. For e.g. "MyPackage-1.2.zip". 

Now, when using satis for hosting these packages, it uses the same code for archiving composer packages implemented at https://github.com/composer/composer/blob/master/src/Composer/Package/Archiver/ArchiveManager.php

In the implementation, getPackageFilename() adds the distReference info to the file name, which makes the zip file created at the end to be weird. Like "jay-logger-1.2-MyPackage-1.2.zip.tar". I am not sure if there is any other use of dist reference in Artifact Repository, but this would stop causing that issue.
Shorter boolean conversion
Merge pull request #2897 from jaypatel512/patch-1

Removing dist reference info from Artifact Repository