Improve the invalid 'BAM\1' magic number error message, and also print it when no bytes can be read from the alleged BAM file, e.g., in the common user error case when a SAM file has accidentally been supplied.
Improve the invalid 'BAM\1' magic number error message, and also print it
when no bytes can be read from the alleged BAM file, e.g., in the common
user error case when a SAM file has accidentally been supplied.


git-svn-id: ba63ac760bf0f03e6bf5520b5300f1a364b8a096@539 fd675618-d7d1-4fc3-a54f-e58cce934862

pjotrp/samtools,pjotrp/samtools,pjotrp/samtools