Allow SoftwareSerial to share RX and TX pins. [imported]

This is [Issue 1022](http://code.google.com/p/arduino/issues/detail?id=1022) moved from a Google Code project.
Added by 2012-08-30T14:00:13.000Z by [dmel...@gmail.com](http://code.google.com/u/107726014984682000895/).
Please review that bug for more context and additional comments, but update this bug.

Original labels: Type-Enhancement, Priority-Medium, Component-SoftwareSerial
### Original description

**What change would like to see?**

From Ed Baafi. The ability for SoftwareSerial to use the same pin for RX and TX (half-duplex). See: https://github.com/Modkit/Arduino/commits/new-extension for a possible implementation.

It would be good if this worked well / simply if you only wanted to either transmit or receive, but not both.

**Why?**

To reduce pin usage.

**Would this cause any incompatibilities with previous versions? If so, how**
**can these be mitigated?**