Force rebuild of library when using mklib directly

With this commit:
- when using plumed mklib the library is always built, even if already present
- when using LOAD FILE=file.cpp, the library is only built if missing

I think this would avoid version mistake in users calling plumed mklib
directly. In addition, it makes plumed mklib work as in v2.9. The only
exception is when called via LOAD, where we force the use of a versioned
name

scripts/mklib.sh

@@ -12,7 +12,7 @@ if [ "$1" = --help ] ; then
 fi
 
 if [ "$1" = --options ] ; then
-  echo "--description --options --help -o"
+  echo "--description --options --help -o -n"
   exit 0
 fi
 
@@ -27,6 +27,7 @@ source "$PLUMED_ROOT"/src/config/compile_options.sh
 
 prefix=""
 lib=""
+no_clobber=""
 files=() # empty array
 for opt
 do
@@ -37,6 +38,8 @@ do
       prefix="--out=";;
     (--out=*)
       lib="${prefixopt#--out=}";;
+    (-n)
+      no_clobber=yes;;
     (-*)
       echo "ERROR: Unknown option $opt. Use --help for help."
       exit 1 ;;
@@ -66,6 +69,10 @@ do
   fi
 done
 
+if test -z "$no_clobber" ; then
+  recompile=yes
+fi
+
 if test $recompile = no ; then
   echo "$lib is already up to date"
   exit 0
@@ -148,5 +155,9 @@ fi
 
 eval "$link_command" "$PLUMED_MKLIB_LDFLAGS" $objs -o "$tmpdir/$lib"
 
-# || true is necessary with recent coreutils
-mv -n "$tmpdir/$lib" $lib || true
+if test -n "$no_clobber" ; then
+  # || true is necessary with recent coreutils
+  mv -n "$tmpdir/$lib" $lib || true
+else
+  mv "$tmpdir/$lib" $lib
+fi

src/core/PlumedMain.cpp

@@ -1261,7 +1261,7 @@ void PlumedMain::load(const std::string& fileName) {
 // full path command, including environment setup
 // this will work even if plumed is not in the execution path or if it has been
 // installed with a name different from "plumed"
-      std::string cmd=config::getEnvCommand()+" \""+config::getPlumedRoot()+"\"/scripts/mklib.sh -o "+libName+" "+fileName;
+      std::string cmd=config::getEnvCommand()+" \""+config::getPlumedRoot()+"\"/scripts/mklib.sh -n -o "+libName+" "+fileName;
 
       if(std::getenv("PLUMED_LOAD_ACTION_DEBUG")) log<<"Executing: "<<cmd;
       else log<<"Compiling: "<<fileName<<" to "<<libName;