Fix BookMergingTests

Two tests were failing on my machine because Mercurial read the ~/.hgrc
file and couldn't load some enable extensions. This change sets the
HGRCPATH environment variable to the empty path which prevents loading
the ~/.hgrc file.
Fix case of bloomCollection file extension

File names on Linux are case sensitive.
Merge pull request #91 from ermshiperete/FixChorusTests

Fix BookMergingTests
Merge pull request #93 from ermshiperete/FixCollectionCase

Fix case of bloomCollection file extension