Use std::vector of const char* instead of std::string where meaningful

This avoids additional string allocation

gnucash/import-export/test/gtest-import-backend.cpp

@@ -248,7 +248,7 @@ TEST_F(ImportBackendBayesTest, CreateTransInfo)
 
     // check tokens created from transaction
     EXPECT_CALL(imap, findAccountBayes(AllOf(
-            Each(Not(IsEmpty())),                // tokens must not be empty strings
+            Each(Not(StrEq(""))),                // tokens must not be empty strings
             Each(Not(HasSubstr(" "))),           // tokens must not contain separator
             Not(HasDuplicates()),                // tokens must be unique
             Contains(StrEq(local_day_of_week)),  // tokens must contain local day of week

libgnucash/engine/mocks/gmock-Account.cpp

@@ -85,7 +85,7 @@ gnc_account_imap_find_account_bayes (
         GList *tokens)
 {
     // \todo use std::list instead of std::vector, since GList is a double-linked list like std::list
-    std::vector<std::string> tokenVec;
+    std::vector<const char*> tokenVec;
 
     for (auto token = tokens; token; token = token->next)
     {
@@ -102,7 +102,7 @@ gnc_account_imap_add_account_bayes (
         Account *acc)
 {
     // \todo use std::list instead of std::vector, since GList is a double-linked list like std::list
-    std::vector<std::string> tokenVec;
+    std::vector<const char*> tokenVec;
 
     for (auto token = tokens; token; token = token->next)
     {

libgnucash/engine/mocks/gmock-Account.h

@@ -62,8 +62,8 @@ public:
 
     MOCK_METHOD2(findAccount, Account *(const char*, const char*));
     MOCK_METHOD3(addAccount, void(const char*, const char*, Account*));
-    MOCK_METHOD1(findAccountBayes, Account *(std::vector<std::string>));
-    MOCK_METHOD2(addAccountBayes, void(std::vector<std::string>, Account*));
+    MOCK_METHOD1(findAccountBayes, Account *(std::vector<const char*>));
+    MOCK_METHOD2(addAccountBayes, void(std::vector<const char*>, Account*));
 };
 
 #endif