Three small typos

line 14 : to contain all points from the origin layer.  ----> 'origin' should be 'original'

line 30 : Since the selction is not  ----> 'selction' should be 'selection'

line 32 : only a geoalgorithm algorithms can be ----> double wording, 'algorithms' can be left out
Merge pull request #420 from DiGro/patch-5

Three small typos