Add -b parameter to samtools merge manpage
Update samtools.1
Match style for FILE option
Alternate syntax for samtools merge.

Providing a FILE to the -b option for samtools merge overrides any file selection made at the command line, I have added an alternative syntax line in the documentation to try and clarify this.
Alternate syntax for samtools merge in stderr message
Clarify list is not a literal
Match samtools merge manpage and stderr syntax
Merge branch 'patch-1' of https://github.com/SamStudio8/samtools into merge_unioninput

Adjust patch to fit in with changes made to usage.