support process substitution <(cmd) and >(cmd)

[christianparpart]

support bash-like process substitution

syntax

<(command)

>(command)

From the bash man-page:

Process Substitution
    Process  substitution  allows  a  process's  input or output to be 
    referred to using a filename.  It takes the form of <(list) or >(list). 
    The process list is run asynchronously, and its input or output appears 
    as a filename.  This filename is passed  as  an    
    argument  to  the  current command as the result of the expansion.  
    If the >(list) form is used, writing to the file will provide    
    input for list.  If the <(list) form is used, the file passed as an 
    argument should  be  read  to  obtain  the  output  of  list.    
    Process substitution is supported on systems that support named pipes
    (FIFOs) or the /dev/fd method of naming open files.

    When available, process substitution is performed simultaneously with 
    parameter and variable expansion, command substitution, 
    and arithmetic expansion.