added -prec option, default 10. Updated unit tests for merge, map, jaccard. Accept stdin by default in merge.

in order to make this compile with clang on FreeBSD 10.

It was correctly identifying reads whose “paired” flag was set, but then
it was incorrectly skipping over the read-pair that follows such an
incorrect read.

Also added a test for this behavior.

Remove extra parentheses that clang thinks are there to prevent a
different warning for "if (numConsumedByB = 0) /*assignment intended*/".
Use 0 instead of NULL to initialise non-pointers.
Only const *integral or enumeration* static data members can be portably
initialised within the class definition.

...so that namespace "std" already exists when we try to use it,
as it will have been declared by the standard headers #included.
Doing otherwise elicits a warning from clang.