Start stubbing out cache_dump
WIP on cache tools
some work on cache_restore
mapping_array.cc
hint_array pack/unpack
Update Gemfile.lock
Fix bad thinp_xml command line
Test for missing input file
Fixup some feature tests that need metadata.bin present

They were failing for the wrong reason.
Move check_file_exists() to file_utils.{h,cc}
[thin_restore] check the input file exists.

Previously we were hanging if it didn't
bump version to 0.2.7