getPrmDflt

 Helper to set default values (if not already set) of parameter struct.

 Takes input parameters and a list of 'name'/default pairs, and for each
 'name' for which prm has no value (prm.(name) is not a field or 'name'
 does not appear in prm list), getPrmDflt assigns the given default
 value. If default value for variable 'name' is 'REQ', and value for
 'name' is not given, an error is thrown. See below for usage details.

 USAGE (nargout==1)
  prm = getPrmDflt( prm, dfs, [checkExtra] )

 USAGE (nargout>1)
  [ param1 ... paramN ] = getPrmDflt( prm, dfs, [checkExtra] )

 INPUTS
  prm          - param struct or cell of form {'name1' v1 'name2' v2 ...}
  dfs          - cell of form {'name1' def1 'name2' def2 ...}
  checkExtra   - [0] if 1 throw error if prm contains params not in dfs
                 if -1 if prm contains params not in dfs adds them

 OUTPUTS (nargout==1)
  prm    - parameter struct with fields 'name1' through 'nameN' assigned

 OUTPUTS (nargout>1)
  param1 - value assigned to parameter with 'name1'
   ...
  paramN - value assigned to parameter with 'nameN'

 EXAMPLE
  dfs = { 'x','REQ', 'y',0, 'z',[], 'eps',1e-3 };
  prm = getPrmDflt( struct('x',1,'y',1), dfs )
  [ x y z eps ] = getPrmDflt( {'x',2,'y',1}, dfs )

 See also INPUTPARSER

 Piotr's Computer Vision Matlab Toolbox      Version 2.60
 Copyright 2014 Piotr Dollar.  [pdollar-at-gmail.com]
 Licensed under the Simplified BSD License [see external/bsd.txt]