tool: overwrite instead of append when using -D

This commit fixes a bug, in which the tool appends to a text file
instead of overwriting it, when a previous transfer took place.

See curl#4753
See curl#4762
Fixes curl#10074
Closes curl#10079

src/tool_operate.c

@@ -969,7 +969,7 @@ static CURLcode single_transfer(struct GlobalConfig *global,
           /* open file for output: */
           if(strcmp(config->headerfile, "-")) {
             FILE *newfile;
-            newfile = fopen(config->headerfile, per->prev == NULL?"wb":"ab");
+            newfile = fopen(config->headerfile, "wb+");
             if(!newfile) {
               warnf(global, "Failed to open %s\n", config->headerfile);
               result = CURLE_WRITE_ERROR;

tests/data/Makefile.inc

@@ -248,7 +248,7 @@ test2500 \
 test3000 test3001 test3002 test3003 test3004 test3005 test3006 test3007 \
 test3008 test3009 test3010 test3011 test3012 test3013 test3014 test3015 \
 test3016 test3017 test3018 test3019 test3020 test3021 test3022 test3023 \
-test3024 test3025 test3026 test3027 test3028 \
+test3024 test3025 test3026 test3027 test3028 test3029 \
 \
 test3100 test3101 \
 test3200

tests/data/test3029

@@ -0,0 +1,59 @@
+<testcase>
+<info>
+<keywords>
+HTTP
+</keywords>
+</info>
+
+#
+# Server-side
+<reply>
+<data>
+HTTP/1.1 200 OK
+Date: Tue, 09 Nov 2010 14:49:00 GMT
+Server: test-server/fake
+Last-Modified: Tue, 13 Jun 2000 12:10:00 GMT
+ETag: "21025-dc7-39462498"
+Accept-Ranges: bytes
+Content-Length: 6
+Connection: close
+Content-Type: text/html
+Funny-head: yesyes
+
+-foo-
+</data>
+</reply>
+
+#
+# Client-side
+<client>
+<server>
+http
+</server>
+ <name>
+HTTP GET with overwriting a header file
+ </name>
+ <command>
+-D log/heads%TESTNUMBER http://%HOSTIP:%HTTPPORT/%TESTNUMBER --next -D log/heads%TESTNUMBER http://%HOSTIP:%HTTPPORT/%TESTNUMBER
+</command>
+</client>
+
+#
+# Verify data after the test has been "shot"
+<verify>
+<file1 name="log/heads%TESTNUMBER" mode="text">
+HTTP/1.1 200 OK
+Date: Tue, 09 Nov 2010 14:49:00 GMT
+Server: test-server/fake
+Last-Modified: Tue, 13 Jun 2000 12:10:00 GMT
+ETag: "21025-dc7-39462498"
+Accept-Ranges: bytes
+Content-Length: 6
+Connection: close
+Content-Type: text/html
+Funny-head: yesyes
+
+</file1>
+
+</verify>
+</testcase>