Inheritance/Extend issue when using extend: 'string'

[gugakatsi]

If you extend a component which extends other components via string, inheritance messes up, it doesn't works.

example:

baseCompA  = { 
   extend: 'Grid',
   props: { ... }
}

aBasedCompB = {
  extend: baseCompA,
  props: { ... }
}

basedCompA loses 'Grid' inheritance. If you change 'Grid' with object Grid {}, It will work as usual.