Add support for pre-Casava 1.8 illumina headers

http://en.wikipedia.org/wiki/FASTQ_format#Illumina_sequence_identifiers
Before Casava 1.8, the nth member of a pair-end or mate pair read was encoded following a slash: e.g. "@HWUSI-EAS100R:6:73:941:1973#0/1"
After Casava 1.8, this follows a space
e.g. "@EAS139:136:FC706VJ:2:2104:15343:197393 1:Y:18:ATCACG"