Update DBEntryAdaptor.pm

Modified the checks for whether the xrefs are stored to identify if the dbID parameter is present, otherwise the xref gets stored.

Feature 84/test var methods

slice.t in order to exclude it from sqlite tests because there are
problems creating sqlite db for variation.

Fix for sub_Slice when slice->start is <1

Use Feature::species() as the only source for species name

- Modified harness to use $ENSDIR as the root dir if available

Update insert sql for protein_feature to avoid duplicate unique keys

Support g. in a location string and some comments

Extending support so locations like X:g.1-10 are parsed as a genomic
coordinate. Also added some comments as the regular expressions are
slightly cryptic.

If you need to explicitly exclude a file it should be pathed directly to
the file. Otherwise you will ignore any occurance of the path in your
source tree. Chances of this one causing a problem are low but it's
something to be aware of

Make stable_id version nullable

Added an extra check onto the condition type in the API as there are some strings that have the text value '0'. These were then getting returned to the user via the API as ''.