2 (very small) pull-requests

[Thomas Neumann]

Hello

2 more pull requests which seem very trivial on their on, but follow the 
general desire to get rid of as many global variables as possible. While
making these variables local does not have an immediate impact it should
change the reader's mindset from 'this one is global - someone else also
uses this variable' to 'this variable is only relevant inside this file'
- let's not waste precious brainpower by making the reader believe these
variables are used somewhere else too when in fact they aren't.


 https://github.com/faiproject/fai/pull/19
 convert global variable %FAI::dev_alias into lexical variable

 https://github.com/faiproject/fai/pull/20
 convert global variable %FAI::partition_table_deps into lexical variable  


The long term goal behind these changes is to convert the pseudomodules 
'Parser.pm', 'Volumes.pm' etc. into true modules with their own private 
namespace (instead of  lumping everything together into 'package FAI').

bye
thomas