Run configure scripts in the shell

[dennis95]

Features needed in the shell that are used by configure scripts:

• [x] : builtin
• [x] redirection needs to work with all commands
• [x] case statements
• [x] command substitution
• [x] set builtin
• [x] eval builtin
• [x] exec builtin
• [x] shell functions
• [x] here-documents

Also some utilities like sed and grep are needed.

[dennis95]

Redirections have now been implemented for compound commands and builtins.

[dennis95]

All shell features originally listed in this issue have now been implemented. What is missing to successfully run configure scripts are some utilities like sed, grep, awk and expr.

Another thing that is needed to fully run the scripts is the trap shell builtin. Implementing that one correctly is tricky because I first need to figure out how to properly handle signals in the shell. However trap is not necessary for the important part of configure scripts and only prints some information to the log.

[dennis95]

Done. Simple configure scripts can now be run without workarounds.