Refactored fork/exec code

In preparation for implementing piping multiple commands.
Added loop in fork to parse piped commands
Added some warning flags
Rewrote parseUserInput without strtok
Refactored fork/exec code into a recursive call

Works so far.  Commands still aren't piped together yet though.  Right
now they still execute sequentially but it's within the recursive
function.  Win!
Fixed some memory allocation problems
Made some more memory cleanups
Memory cleanup
Fixed a typo that caused a compilation error
Piping works, but error checking needs improvement, etc
Some cleanups
Temp piping solution. It kinda works but still really buggy.
Merge branch 'piping' of github.com:kbara/_dash into kbara-piping

Conflicts:
	Makefile
	dash.c