Better warning in case of `@form`

When having a problem like:
```
/** \file */

/**
 * The fie
 *
 * @form: the new format
 * @content: the content of the form
 *
 * Sets @form content to be @content.
 *
 * \f$ \alpha \f$ \f[ \beta \f]
 */
void fie(char *form, char *content);
```
we get warnings like:
```
.../aa.h:5: warning: Wrong formula id -1
.../aa.h:6: warning: Found unknown command '\content'
.../aa.h:8: warning: Wrong formula id -1
.../aa.h:8: warning: Found unknown command '\content'
```

The `@form:` is in RST analogue to the doxygen `@param form` but not understood by doxygen.
The result is that it is seen as an formula as doxygen translates the formula commands to `\form`.
For `@content` is handled properly as this is not a doxygen command.

In this patch a more unique name is chosen so these type of conflicts don't appear (that easy). The resulting, better, warnings are now:
```
.../aa.h:5: warning: Found unknown command '\form'
.../aa.h:6: warning: Found unknown command '\content'
.../aa.h:8: warning: Found unknown command '\form'
.../aa.h:8: warning: Found unknown command '\content'
```

1 files changed, 2 insertions, 2 deletions

diff --git a/src/commentscan.l b/src/commentscan.l
index 6e7d373..0494d88 100644
--- a/src/commentscan.l
+++ b/src/commentscan.l
@@ -622,12 +622,12 @@ static QCString addFormula()
     f = new Formula(fText);
     Doxygen::formulaList->append(f);
     Doxygen::formulaDict->insert(fText,f);
-    formLabel.sprintf("\\form#%d",f->getId());
+    formLabel.sprintf("\\_fakeform#%d",f->getId());
     Doxygen::formulaNameDict->insert(formLabel,f);
   }
   else
   {
-    formLabel.sprintf("\\form#%d",f->getId());
+    formLabel.sprintf("\\_fakeform#%d",f->getId());
   }
   int i;
   for (i=0;i<formulaNewLines;i++) formLabel+="@_fakenl"; // add fake newlines to