Fix issue where VSCode makefile extension can delete files

The problem is that VSCode's make extension, in order to determine
some information about the project, runs
```
make --dry-run --always-make
```
which despite its name will actually try to remake the configure/*
files. Running `installEpics.pl` on these will delete them first,
then try copy them, resulting in an error.

src/tools/installEpics.pl

@@ -22,6 +22,7 @@
 use Getopt::Std;
 use File::Path;
 use File::Copy;
+use Cwd 'abs_path';
 
 my $tool = basename($0);
 my $mode = 0755;
@@ -57,6 +58,9 @@
     my $temp   = "$install_dir/TEMP.$name.$$";
     my $target = "$install_dir/$name";
 
+    # Don't try to install the file if it already exists
+    next if abs_path($source) eq abs_path($target);
+
     if (-f $target) {
         next if -M $target < -M $source and -C $target < -C $source;
         # Remove old target, making sure it is deletable first