Removing etc1 from build for javascript platform.

Based on inputs from reduz
1) Made etc1 optional driver and default yes.
2) Reverted the hack in rg_etc1.cpp
3) Disabled etc1 for javascript plaform.

SConstruct

@@ -111,6 +111,7 @@ opts.Add('jpg','JPG Image loader support (yes/no)','yes')
 opts.Add('webp','WEBP Image loader support (yes/no)','yes')
 opts.Add('dds','DDS Texture loader support (yes/no)','yes')
 opts.Add('pvr','PVR (PowerVR) Texture loader support (yes/no)','yes')
+opts.Add('etc1','etc1 Texture compression support (yes/no)','yes')
 opts.Add('builtin_zlib','Use built-in zlib (yes/no)','yes')
 opts.Add('openssl','Use OpenSSL (yes/no/builtin)','no')
 opts.Add('musepack','Musepack Audio (yes/no)','yes')

drivers/etc1/rg_etc1.cpp

@@ -1918,11 +1918,7 @@ done:
                      int v = etc1_decode_value(diff, inten, selector, packed_c);
                      uint err = labs(v - static_cast<int>(color));
 		     //printf("err: %d - %u = %u\n",v,color,err);
-                    #ifdef JAVASCRIPT_ENABLED
-                     if (err < best_error || best_error == cUINT32_MAX)
-                    #else
                      if (err < best_error)
-                    #endif 
                      {
                         best_error = err;
                         best_packed_c = packed_c;

platform/javascript/detect.py

@@ -36,6 +36,7 @@ def get_flags():
 		('squish', 'no'),
 		('speex', 'no'),
 		('old_scenes', 'no'),
+		('etc1', 'no'),
 #		('default_gui_theme', 'no'),
 
 		#('builtin_zlib', 'no'),