compat/regex: fix spelling and grammar in comments

Some of these were found using Lucas De Marchi's codespell tool.
Others noticed by Eric Sunshine.

Helped-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Acked-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

compat/regex/regcomp.c

@@ -2095,7 +2095,7 @@ peek_token_bracket (re_token_t *token, re_string_t *input, reg_syntax_t syntax)
 
 /* Entry point of the parser.
    Parse the regular expression REGEXP and return the structure tree.
-   If an error is occured, ERR is set by error code, and return NULL.
+   If an error has occurred, ERR is set by error code, and return NULL.
    This function build the following tree, from regular expression <reg_exp>:
 	   CAT
 	   / \
@@ -3715,7 +3715,7 @@ build_charclass_op (re_dfa_t *dfa, RE_TRANSLATE_TYPE trans,
 /* This is intended for the expressions like "a{1,3}".
    Fetch a number from `input', and return the number.
    Return -1, if the number field is empty like "{,1}".
-   Return -2, If an error is occured.  */
+   Return -2, if an error has occurred.  */
 
 static int
 fetch_number (re_string_t *input, re_token_t *token, reg_syntax_t syntax)

compat/regex/regex.c

@@ -22,7 +22,7 @@
 #include "config.h"
 #endif
 
-/* Make sure noone compiles this code with a C++ compiler.  */
+/* Make sure no one compiles this code with a C++ compiler.  */
 #ifdef __cplusplus
 # error "This is C code, use a C compiler"
 #endif

compat/regex/regex_internal.c

@@ -1284,7 +1284,7 @@ re_node_set_merge (re_node_set *dest, const re_node_set *src)
 
 /* Insert the new element ELEM to the re_node_set* SET.
    SET should not already have ELEM.
-   return -1 if an error is occured, return 1 otherwise.  */
+   return -1 if an error has occurred, return 1 otherwise.  */
 
 static int
 internal_function
@@ -1341,7 +1341,7 @@ re_node_set_insert (re_node_set *set, int elem)
 
 /* Insert the new element ELEM to the re_node_set* SET.
    SET should not already have any element greater than or equal to ELEM.
-   Return -1 if an error is occured, return 1 otherwise.  */
+   Return -1 if an error has occurred, return 1 otherwise.  */
 
 static int
 internal_function
@@ -1416,7 +1416,7 @@ re_node_set_remove_at (re_node_set *set, int idx)
 
 
 /* Add the token TOKEN to dfa->nodes, and return the index of the token.
-   Or return -1, if an error will be occured.  */
+   Or return -1, if an error has occurred.  */
 
 static int
 internal_function