Fix a size comparison

To correctly compare two sizes, each specified using a number with a letter suffix (M, G, &c), you have to multiply each number by the factor implied by the suffix, not divide it.  The current code would accept a change from e.g. 1G to 1M as an increase.
Merge pull request #58 from tih/patch-1

Fix a size comparison
Fix exec that was missing a path attribute
Add autorequire for the volume_group
Merge pull request #59 from adamcrews/fix_exec_path

Fix exec that was missing a path attribute
Merge pull request #61 from adamcrews/autorequire_vg

Add autorequire for the volume_group
Prepare a 0.3.2 release.
Merge pull request #62 from apenney/032-release

Prepare a 0.3.2 release.
Use fully qualified volume paths
Implement 'instances' method for all LVM resources

This method makes it possible to use constructs like:
  resources { 'physical_volume': purge => true, noop => true, }
  resources { 'logical_volume':  purge => true, noop => true, }
  resources { 'volume_group':    purge => true, noop => true, }
Set default LV unit size to MB