ENH: minor improvements to environment

- handle sourcing bashrc with a relative path (issue #383)
- handle sourcing from bash and zsh.
  Still need manual intervention when sourcing dash, sh, or ksh.
- replace grep in etc/cshrc with sed only
- logical instead of physical path for WM_PROJECT_DIR (issue #431).
  Doesn't seem to be possible for csh/tcsh.

  * Continue using physical locations when comparing directories,
    but not for the top-level FOAM_INST_DIR, WM_PROJECT_DIR.

- relocate WM_CC, WM_CXX overrides from etc/config.*/compiler
  to etc/config.*/settings to ensure that they are left untouched
  when etc/config.sh/compiler is sourced while making third-party
  packages (eg, gcc, llvm, CGAL).

- provide fallback FOAM_TUTORIALS setting in RunFunctions

STYLE: remove "~OpenFOAM" fallback as being too rare, non-obvious

etc/config.csh/example/compiler

@@ -30,21 +30,13 @@
 #
 #------------------------------------------------------------------------------
 
-# Modified compiler settings
+# Modify/override compiler settings
 switch ("$WM_COMPILER")
-case Gcc46:
-case Gcc46++0x:
-    set gcc_version=gcc-4.6.0
-    set gmp_version=gmp-5.0.1
-    set mpfr_version=mpfr-2.4.2
-    set mpc_version=mpc-0.8.1
-    breaksw
-case Gcc45:
-case Gcc45++0x:
-    set gcc_version=gcc-4.5.2
-    set gmp_version=gmp-5.0.1
-    set mpfr_version=mpfr-2.4.2
-    set mpc_version=mpc-0.8.1
+case Gcc70:
+    set gcc_version=gcc-7.0.0
+    set gmp_version=gmp-6.1.2
+    set mpfr_version=mpfr-3.1.5
+    set mpc_version=mpc-1.0.3
     breaksw
 endsw