libs: made error message clearer and more consistent

lib/filefct.sh

@@ -152,7 +152,7 @@ isdirempty()
     dir=$1
 
     if [[ -f $dir ]]; then
-        prnt E "isdirempty():The given parameter is not a directory."
+        prnt E "isdirempty(): The given parameter is not a directory."
         die 15
     fi
     if [[ ! -d $dir ]]; then
@@ -177,7 +177,7 @@ patchfile()
     local workfile=${dstfile}.work
 
     if [[ ! -s $srcfile ]]; then
-        prnt E "The source file is empty, is not a file or don't exists!"
+        prnt E "patchfile(): Source file is empty, is not a file or don't exists!"
         die 10
     fi
 
@@ -218,7 +218,7 @@ file_exists()
     prnt I "Checking $@ files existance..."
     for f in $@; do
         if [[ ! -f $(select_file $f) ]]; then
-            prnt E "The $f file is missing, cannot continue."
+            prnt E "file_exists(): The $f file is missing, can't continue."
             die 10
        fi
     done