Spanish: handle lack of cents part for whole-number currency values

[bryananderson]

Fixes bug in Spanish currency handling when there is no cents part of the value

Changes proposed in this pull request:

• Now we check if there is a cents part before we try to access it

Status

• READY
• HOLD
• WIP (Work-In-Progress)

How to verify this change

Run tests (added integer test cases)

[bryananderson]

I also want to note that base.py here calls parse_currency_parts() here which will assume that an integer value means cents rather than dollars/euros/etc--this is not intuitive to me at all, is it the desired behavior?

[coveralls]

coverage: 98.118%. remained the same
when pulling 21c6eac on bryananderson:spanish-no-cents
into 46c9580 on savoirfairelinux:master.