Use bash not sh in launch scripts.

prism.darwin and xprism.linux declared #!/bin/sh but used bash-specific
syntax (arrays, C-style for loops, [[ ]] tests). prism.linux already used
#!/bin/bash. Switch all three to #!/usr/bin/env bash for consistency.

Author: davexparker

prism/src/bin/prism.darwin

@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/usr/bin/env bash
 
 # Startup script for PRISM (Mac OS X)
 

prism/src/bin/prism.linux

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 # Startup script for PRISM (Linux/Solaris)
 

prism/src/bin/xprism.linux

@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/usr/bin/env bash
 
 # Startup script for PRISM GUI (Linux/Solaris)