Implement internaltcl functionality

When passing '-internaltcl' to netgen, it will evaluate a preprocessed
tcl string instead of loading ng.tcl.
The string is stored in the file onetcl.cpp, which is generated by onetcl.py

ng/ng.tcl

@@ -1,4 +1,4 @@
-lappend auto_path $env(NETGENDIR) 
+catch {lappend auto_path $env(NETGENDIR) }
 
 set batchmode [Ng_GetCommandLineParameter batchmode]
 if {$batchmode=="undefined"} {

ng/onetcl.py

@@ -0,0 +1,44 @@
+import glob
+import functools
+
+# load all tcl files in current folder
+tclfiles = {}
+for fname in glob.glob('*.tcl'):
+    tclfiles[fname] = open(fname,'r').read()
+
+# do a topological sorting (such that if a.tcl is including b.tcl,
+# a will come after b in the sorted list)
+fnames = list(tclfiles.keys())
+fnames.sort(key=functools.cmp_to_key( lambda x,y: tclfiles[x].find('/'+y) ))
+
+# replace all occurences of 'source bla.tcl' with the code of bla.tcl
+for f in fnames:
+    for g in fnames:
+        if(tclfiles[f].find('/'+g) >= 0):
+            tclfiles[f] = tclfiles[f].replace("source ${ngdir}/"+g, tclfiles[g])
+
+# write a cpp file containing the result of ng.tcl
+onetclcpp = open("onetcl.cpp",'w')
+onetclcpp.write('const char * ngscript[] = {""'+'\n');
+
+# make sure to remove comments (and if lines with comments end with '\' also the next line(s) )
+skip_next = False # flag to indicate that the next line should be removed
+for line in tclfiles["ng.tcl"].split('\n'):
+    line = line.strip()
+    if len(line)==0:
+        skip_next = False
+        continue
+    if skip_next:
+        # skip as long as lines end with '\'
+        skip_next = line[-1]=='\\'
+        continue
+    if(line.find('#')>-1):
+        # comment found (not necessarily the whole line)
+        skip_next = line[-1]=='\\'
+        line = line[:line.find('#')]
+    if len(line)>0:
+        s = ',"' + line.replace('\\', r'\\').replace('"', r'\"') + '\\n"\n'
+        onetclcpp.write(s)
+
+onetclcpp.write('};'+'\n');
+onetclcpp.close();