Fix EPW-related issues

@macumber This pull request should resolve #997. Here's a list of the changes:

* OpenStudio will now accept weather files that initially look like AMY files but have a date period "first day of the week" that does not match the data in the file. A warning is generated and OpenStudio should (hopefully) treat the file as a TMY file from then on.
* The data period is now used to generate the minutes for the weather data points, so the 0/60 thing is not an issue.
* I added an additional unit test using an international file (CHN_Guangdong.Shaoguan.590820_CSWD.epw)

As of now, all 2574 weather files available from DOE can be read by OpenStudio.
@jasondegraw in the future prefer: return boost::none;