Improve relative paths for file import.

Don't break on case-sensitive filesystems, and don't require an explicit
regen after initial save of the assembly.

src/file.cpp

@@ -255,7 +255,10 @@ void SolveSpace::SaveUsingTable(int type) {
 
 bool SolveSpace::SaveToFile(char *filename) {
     // Make sure all the entities are regenerated up to date, since they
-    // will be exported.
+    // will be exported. We reload the imported files because that rewrites
+    // the impFileRel for our possibly-new filename.
+    SS.later.showTW = true;
+    SS.ReloadAllImported();
     SS.GenerateAll(0, INT_MAX);
 
     fh = fopen(filename, "wb");

src/solvespace.cpp

@@ -319,19 +319,22 @@ void SolveSpace::AddToRecentList(char *file) {
 }
 
 bool SolveSpace::GetFilenameAndSave(bool saveAs) {
+    char prevSaveFile[MAX_PATH];
+    strcpy(prevSaveFile, saveFile);
 
-    char newFile[MAX_PATH];
-    strcpy(newFile, saveFile);
-    if(saveAs || strlen(newFile)==0) {
-        if(!GetSaveFile(newFile, SLVS_EXT, SLVS_PATTERN)) return false;
+    if(saveAs || strlen(saveFile)==0) {
+        if(!GetSaveFile(saveFile, SLVS_EXT, SLVS_PATTERN)) return false;
+        // need to get new filename directly into saveFile, since that
+        // determines impFileRel path
     }
 
-    if(SaveToFile(newFile)) {
-        AddToRecentList(newFile);
-        strcpy(saveFile, newFile);
+    if(SaveToFile(saveFile)) {
+        AddToRecentList(saveFile);
         unsaved = false;
         return true;
     } else {
+        // don't store an invalid save filename
+        strcpy(saveFile, prevSaveFile);
         return false;
     }
 }

src/util.cpp

@@ -60,7 +60,8 @@ void MakePathRelative(const char *basep, char *pathp)
     for(i = 0; i < sections; i++) {
         strcat(out, "../");
     }
-    strcat(out, path+com);
+    // comparison is case-insensitive, but output preserves input case
+    strcat(out, pathp+com);
 
     strcpy(pathp, out);
 }