Merge branch 'develop'

- Make options with implicit value use next token, like it did
  before.
- Support boost::optional option variables.
- Fix syntax error with BOOST_NO_EXCEPTIONS
- Fix uninitlized position_key in some cases.

include/boost/program_options/errors.hpp

@@ -110,13 +110,13 @@ namespace boost { namespace program_options {
         std::map<std::string, string_pair > m_substitution_defaults;
 
     public:
-		/** template with placeholders */
-		std::string m_error_template;
+        /** template with placeholders */
+        std::string m_error_template;
 
-		error_with_option_name(const std::string& template_,
-                              const std::string& option_name = "",
-                              const std::string& original_token = "",
-                              int option_style               = 0);
+        error_with_option_name(const std::string& template_,
+                               const std::string& option_name = "",
+                               const std::string& original_token = "",
+                               int option_style = 0);
 
         /** gcc says that throw specification on dtor is loosened 
          *  without this line                                     

test/exception_txt_test.cpp

@@ -152,7 +152,7 @@ void test_invalid_option_value_exception_msg()
 {
     options_description desc;
     desc.add_options()
-        ("int-option,d", value< int >(),	"An option taking an integer")
+        ("int-option,d", value< int >(),        "An option taking an integer")
     ;
 
     vector<vector<const char*> > argv;
@@ -308,7 +308,7 @@ void test_invalid_bool_value_exception_msg()
 {
     options_description desc; 
     desc.add_options()
-        ("bool_option,b",	value< bool>(),	"bool_option")
+        ("bool_option,b",       value< bool>(), "bool_option")
         ;