in build.xml, changed htsjdk.version.property.xml to htsjdk.version.properties

in build.xml, changed htsjdk.version.property.xml to htsjdk.version.properties.

See https://github.com/samtools/htsjdk/issues/99

```
$ ant
Buildfile: /home/lindenb/src/htsjdk/build.xml

write-version-property:
[propertyfile] Creating new property file: /home/lindenb/src/htsjdk/htsjdk.version.properties

init:
(...)

$ cat htsjdk version
#Wed, 17 Sep 2014 20:28:57 +0200

htsjdk-version=1.120
```