`gem search` should not anchor search terms

In response to rubygems/rubygems#166, @drbrain committed rubygems/rubygems@cefe716, which changed `gem search` to default to `--remote` and also to anchor search terms like `gem list`.

IMO this anchoring is a big pain for search usability. I never want anchored terms. This sucks:

```
$ gem search usb

*** REMOTE GEMS ***

usb-detection-sensor (0.2.2)
usbmux (0.0.1)

$ gem search libusb

*** REMOTE GEMS ***

libusb (0.3.4 ruby x64-mingw32 x86-mingw32)
```

So, this branch reverts that change and simply defaults to `--remote` for search. This still satisfies #166, but removes the annoyance of surprise regexp anchors.