Can't import OFX files with missing OFXHEADER

[dtbartle]

Rogers Bank credit card OFX exports are missing the standard OFXHEADER:100 header and instead immediately starts with <OFX>. I suspect this would be easy enough to fix in guessVersion by returning false if b starts with <OFX>. I can work around this easy enough myself by prepending a standard header (i.e. everything parses correctly otherwise).

[aclindsa]

Hah, well that's pretty silly of them.

I'm open to pull requests which handle this while ensuring well-formed OFX doesn't suffer any ill consequences.