Fix history file parsing when fetched from archive

History file format has changed from 9.2 to 9.3 to indicate the WAL record
when timeline branched off. In 9.2, the complete WAL file name was used
while in 9.3 the WAL record is used (like 1/4000090). pg_rman contains a
copy of a function of postgres core code to parse the history file that
was not anymore compatible, leading to errors related to timelines.