Fixed some CCLabelBMFont issues

[moadib]

Font definition field "file" can contain underline character, fixed regexp for that

Modified LabelBMFont for conformity with cocos2d-x.

Without it cocos2d-html can't render correct multiline labels after calling setTextAlignment or setScale and can't handle strings with empty lines.

[moadib]

You can easy reproduce problem with string "Abcdefgh\n\nqwerty\nasad" and changing alignment to Right or Center, also you can add scale.

@linshun It is important :) Look at cocos2d-x, it contains this changes.

[linshun]

The bug of "Font definition field "file" can contain underline character" has been fixed by this commit: a4707bf

[linshun]

About the bug "Without it cocos2d-html can't render correct multiline labels after calling setTextAlignment or setScale and can't handle strings with empty lines", I checked your code with the latest version of Cocos2d-html5 on "develop" branch, and the bug can not be fixed.

[moadib]

I have no time to check it, but this changes allows html5 port of my existing game work same as native version. Anyway, at moment when i was pulled this changes, html5 code doesn't conform native version of labelbmfont.

[linshun]

Thanks. We will track this issue, and fix it in next week.