Allow + for file names in file wizard

Since some people want to use e.g. c++ as extension.

Task-number: QTCREATORBUG-11266
Change-Id: I88686d814f49fcbc794c8c3427ee7251b24fa563
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>

src/libs/utils/filenamevalidatinglineedit.cpp

@@ -98,7 +98,7 @@ void FileNameValidatingLineEdit::setForceFirstCapitalLetter(bool b)
 #define SLASHES "/\\"
 
 static const char notAllowedCharsSubDir[]   = ",^@=+{}[]~!?:&*\"|#%<>$\"'();`' ";
-static const char notAllowedCharsNoSubDir[] = ",^@=+{}[]~!?:&*\"|#%<>$\"'();`' " SLASHES;
+static const char notAllowedCharsNoSubDir[] = ",^@={}[]~!?:&*\"|#%<>$\"'();`' " SLASHES;
 
 static const char *notAllowedSubStrings[] = {".."};