Merge branches 'issue-475-find-mpi', 'issue-463' and 'bump-gcc-version'

Author: zbeekman

install.sh-usage

@@ -1,5 +1,5 @@
   -b --install-branch [arg]   Install the specified repository development branch (Examples: -b trunk or -b gcc-7-branch).
-  -B --list-branches [arg]    List the available branches in the specified package's repository (Example: -B gcc).
+  -B --list-branches [arg]    List the available branches in a package's repository (Currently only '-B gcc' is supported).
   -c --with-c [arg]           Use specified C compiler (Example: -c /usr/local/bin/gcc).
   -C --with-cxx [arg]         Use specified C++ compiler (Example: -C /usr/local/bin/g++).
   -d --debug                  Enable debug mode. 

prerequisites/build-functions/set_or_print_default_version.sh

@@ -27,7 +27,7 @@ set_or_print_default_version()
   # See http://stackoverflow.com/questions/1494178/how-to-define-hash-tables-in-bash
   package_version=(
     "cmake:3.4.0"
-    "gcc:7.2.0"
+    "gcc:7.3.0"
     "mpich:3.2"
     "wget:1.16.3"
     "flex:2.6.0"