bug(select): select menu should not be underlined

[robertmesserle]

In RC2, md-select menus are now underlined. This is breaking a number of layouts and does not appear to be according to spec.

[clshortfuse]

Well, sometimes it's underlined, sometimes it's not. I haven't figured out exactly when, but I believe it should be optional.

material design spec example

The top select isn't underlined, but the bottom one is.

I worked around this by making it optional. See http://codepen.io/shortfuse/pen/oxGowZ

md-select.md-no-border .md-select-value {
  border-bottom-color: transparent !important;
}